f3479816bb
Fix spelling errors in EDAC documentation. Signed-off-by: David S. Peterson <dsp@llnl.gov> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
674 lines
19 KiB
Plaintext
674 lines
19 KiB
Plaintext
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EDAC - Error Detection And Correction
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Written by Doug Thompson <norsk5@xmission.com>
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7 Dec 2005
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EDAC was written by:
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Thayne Harbaugh,
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modified by Dave Peterson, Doug Thompson, et al,
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from the bluesmoke.sourceforge.net project.
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============================================================================
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EDAC PURPOSE
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The 'edac' kernel module goal is to detect and report errors that occur
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within the computer system. In the initial release, memory Correctable Errors
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(CE) and Uncorrectable Errors (UE) are the primary errors being harvested.
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Detecting CE events, then harvesting those events and reporting them,
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CAN be a predictor of future UE events. With CE events, the system can
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continue to operate, but with less safety. Preventive maintenance and
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proactive part replacement of memory DIMMs exhibiting CEs can reduce
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the likelihood of the dreaded UE events and system 'panics'.
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In addition, PCI Bus Parity and SERR Errors are scanned for on PCI devices
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in order to determine if errors are occurring on data transfers.
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The presence of PCI Parity errors must be examined with a grain of salt.
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There are several add-in adapters that do NOT follow the PCI specification
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with regards to Parity generation and reporting. The specification says
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the vendor should tie the parity status bits to 0 if they do not intend
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to generate parity. Some vendors do not do this, and thus the parity bit
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can "float" giving false positives.
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The PCI Parity EDAC device has the ability to "skip" known flaky
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cards during the parity scan. These are set by the parity "blacklist"
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interface in the sysfs for PCI Parity. (See the PCI section in the sysfs
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section below.) There is also a parity "whitelist" which is used as
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an explicit list of devices to scan, while the blacklist is a list
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of devices to skip.
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EDAC will have future error detectors that will be added or integrated
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into EDAC in the following list:
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MCE Machine Check Exception
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MCA Machine Check Architecture
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NMI NMI notification of ECC errors
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MSRs Machine Specific Register error cases
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and other mechanisms.
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These errors are usually bus errors, ECC errors, thermal throttling
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and the like.
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============================================================================
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EDAC VERSIONING
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EDAC is composed of a "core" module (edac_mc.ko) and several Memory
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Controller (MC) driver modules. On a given system, the CORE
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is loaded and one MC driver will be loaded. Both the CORE and
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the MC driver have individual versions that reflect current release
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level of their respective modules. Thus, to "report" on what version
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a system is running, one must report both the CORE's and the
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MC driver's versions.
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LOADING
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If 'edac' was statically linked with the kernel then no loading is
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necessary. If 'edac' was built as modules then simply modprobe the
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'edac' pieces that you need. You should be able to modprobe
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hardware-specific modules and have the dependencies load the necessary core
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modules.
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Example:
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$> modprobe amd76x_edac
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loads both the amd76x_edac.ko memory controller module and the edac_mc.ko
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core module.
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============================================================================
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EDAC sysfs INTERFACE
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EDAC presents a 'sysfs' interface for control, reporting and attribute
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reporting purposes.
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EDAC lives in the /sys/devices/system/edac directory. Within this directory
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there currently reside 2 'edac' components:
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mc memory controller(s) system
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pci PCI status system
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============================================================================
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Memory Controller (mc) Model
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First a background on the memory controller's model abstracted in EDAC.
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Each mc device controls a set of DIMM memory modules. These modules are
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laid out in a Chip-Select Row (csrowX) and Channel table (chX). There can
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be multiple csrows and two channels.
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Memory controllers allow for several csrows, with 8 csrows being a typical value.
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Yet, the actual number of csrows depends on the electrical "loading"
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of a given motherboard, memory controller and DIMM characteristics.
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Dual channels allows for 128 bit data transfers to the CPU from memory.
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Channel 0 Channel 1
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===================================
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csrow0 | DIMM_A0 | DIMM_B0 |
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csrow1 | DIMM_A0 | DIMM_B0 |
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===================================
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===================================
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csrow2 | DIMM_A1 | DIMM_B1 |
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csrow3 | DIMM_A1 | DIMM_B1 |
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===================================
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In the above example table there are 4 physical slots on the motherboard
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for memory DIMMs:
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DIMM_A0
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DIMM_B0
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DIMM_A1
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DIMM_B1
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Labels for these slots are usually silk screened on the motherboard. Slots
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labeled 'A' are channel 0 in this example. Slots labeled 'B'
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are channel 1. Notice that there are two csrows possible on a
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physical DIMM. These csrows are allocated their csrow assignment
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based on the slot into which the memory DIMM is placed. Thus, when 1 DIMM
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is placed in each Channel, the csrows cross both DIMMs.
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Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
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Thus, 2 single ranked DIMMs, placed in slots DIMM_A0 and DIMM_B0 above
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will have 1 csrow, csrow0. csrow1 will be empty. On the other hand,
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when 2 dual ranked DIMMs are similarly placed, then both csrow0 and
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csrow1 will be populated. The pattern repeats itself for csrow2 and
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csrow3.
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The representation of the above is reflected in the directory tree
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in EDAC's sysfs interface. Starting in directory
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/sys/devices/system/edac/mc each memory controller will be represented
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by its own 'mcX' directory, where 'X" is the index of the MC.
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..../edac/mc/
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|->mc0
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|->mc1
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|->mc2
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....
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Under each 'mcX' directory each 'csrowX' is again represented by a
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'csrowX', where 'X" is the csrow index:
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.../mc/mc0/
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|->csrow0
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|->csrow2
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|->csrow3
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....
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Notice that there is no csrow1, which indicates that csrow0 is
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composed of a single ranked DIMMs. This should also apply in both
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Channels, in order to have dual-channel mode be operational. Since
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both csrow2 and csrow3 are populated, this indicates a dual ranked
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set of DIMMs for channels 0 and 1.
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Within each of the 'mc','mcX' and 'csrowX' directories are several
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EDAC control and attribute files.
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============================================================================
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DIRECTORY 'mc'
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In directory 'mc' are EDAC system overall control and attribute files:
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Panic on UE control file:
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'panic_on_ue'
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An uncorrectable error will cause a machine panic. This is usually
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desirable. It is a bad idea to continue when an uncorrectable error
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occurs - it is indeterminate what was uncorrected and the operating
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system context might be so mangled that continuing will lead to further
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corruption. If the kernel has MCE configured, then EDAC will never
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notice the UE.
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LOAD TIME: module/kernel parameter: panic_on_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/panic_on_ue
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Log UE control file:
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'log_ue'
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Generate kernel messages describing uncorrectable errors. These errors
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are reported through the system message log system. UE statistics
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will be accumulated even when UE logging is disabled.
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LOAD TIME: module/kernel parameter: log_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ue
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Log CE control file:
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'log_ce'
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Generate kernel messages describing correctable errors. These
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errors are reported through the system message log system.
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CE statistics will be accumulated even when CE logging is disabled.
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LOAD TIME: module/kernel parameter: log_ce=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ce
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Polling period control file:
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'poll_msec'
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The time period, in milliseconds, for polling for error information.
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Too small a value wastes resources. Too large a value might delay
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necessary handling of errors and might loose valuable information for
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locating the error. 1000 milliseconds (once each second) is about
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right for most uses.
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LOAD TIME: module/kernel parameter: poll_msec=[0|1]
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RUN TIME: echo "1000" >/sys/devices/system/edac/mc/poll_msec
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Module Version read-only attribute file:
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'mc_version'
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The EDAC CORE module's version and compile date are shown here to
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indicate what EDAC is running.
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============================================================================
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'mcX' DIRECTORIES
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In 'mcX' directories are EDAC control and attribute files for
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this 'X" instance of the memory controllers:
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Counter reset control file:
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'reset_counters'
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This write-only control file will zero all the statistical counters
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for UE and CE errors. Zeroing the counters will also reset the timer
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indicating how long since the last counter zero. This is useful
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for computing errors/time. Since the counters are always reset at
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driver initialization time, no module/kernel parameter is available.
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RUN TIME: echo "anything" >/sys/devices/system/edac/mc/mc0/counter_reset
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This resets the counters on memory controller 0
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Seconds since last counter reset control file:
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'seconds_since_reset'
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This attribute file displays how many seconds have elapsed since the
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last counter reset. This can be used with the error counters to
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measure error rates.
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DIMM capability attribute file:
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'edac_capability'
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The EDAC (Error Detection and Correction) capabilities/modes of
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the memory controller hardware.
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DIMM Current Capability attribute file:
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'edac_current_capability'
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The EDAC capabilities available with the hardware
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configuration. This may not be the same as "EDAC capability"
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if the correct memory is not used. If a memory controller is
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capable of EDAC, but DIMMs without check bits are in use, then
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Parity, SECDED, S4ECD4ED capabilities will not be available
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even though the memory controller might be capable of those
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modes with the proper memory loaded.
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Memory Type supported on this controller attribute file:
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'supported_mem_type'
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This attribute file displays the memory type, usually
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buffered and unbuffered DIMMs.
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Memory Controller name attribute file:
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'mc_name'
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This attribute file displays the type of memory controller
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that is being utilized.
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Memory Controller Module name attribute file:
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'module_name'
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This attribute file displays the memory controller module name,
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version and date built. The name of the memory controller
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hardware - some drivers work with multiple controllers and
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this field shows which hardware is present.
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Total memory managed by this memory controller attribute file:
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'size_mb'
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This attribute file displays, in count of megabytes, of memory
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that this instance of memory controller manages.
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Total Uncorrectable Errors count attribute file:
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'ue_count'
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This attribute file displays the total count of uncorrectable
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errors that have occurred on this memory controller. If panic_on_ue
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is set this counter will not have a chance to increment,
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since EDAC will panic the system.
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Total UE count that had no information attribute fileY:
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'ue_noinfo_count'
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This attribute file displays the number of UEs that
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have occurred have occurred with no informations as to which DIMM
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slot is having errors.
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Total Correctable Errors count attribute file:
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'ce_count'
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This attribute file displays the total count of correctable
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errors that have occurred on this memory controller. This
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count is very important to examine. CEs provide early
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indications that a DIMM is beginning to fail. This count
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field should be monitored for non-zero values and report
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such information to the system administrator.
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Total Correctable Errors count attribute file:
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'ce_noinfo_count'
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This attribute file displays the number of CEs that
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have occurred wherewith no informations as to which DIMM slot
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is having errors. Memory is handicapped, but operational,
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yet no information is available to indicate which slot
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the failing memory is in. This count field should be also
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be monitored for non-zero values.
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Device Symlink:
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'device'
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Symlink to the memory controller device
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============================================================================
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'csrowX' DIRECTORIES
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In the 'csrowX' directories are EDAC control and attribute files for
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this 'X" instance of csrow:
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Total Uncorrectable Errors count attribute file:
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'ue_count'
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This attribute file displays the total count of uncorrectable
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errors that have occurred on this csrow. If panic_on_ue is set
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this counter will not have a chance to increment, since EDAC
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will panic the system.
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Total Correctable Errors count attribute file:
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'ce_count'
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This attribute file displays the total count of correctable
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errors that have occurred on this csrow. This
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count is very important to examine. CEs provide early
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indications that a DIMM is beginning to fail. This count
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field should be monitored for non-zero values and report
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such information to the system administrator.
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Total memory managed by this csrow attribute file:
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'size_mb'
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This attribute file displays, in count of megabytes, of memory
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that this csrow contains.
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Memory Type attribute file:
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'mem_type'
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This attribute file will display what type of memory is currently
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on this csrow. Normally, either buffered or unbuffered memory.
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EDAC Mode of operation attribute file:
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'edac_mode'
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This attribute file will display what type of Error detection
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and correction is being utilized.
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Device type attribute file:
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'dev_type'
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This attribute file will display what type of DIMM device is
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being utilized. Example: x4
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Channel 0 CE Count attribute file:
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'ch0_ce_count'
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This attribute file will display the count of CEs on this
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DIMM located in channel 0.
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Channel 0 UE Count attribute file:
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'ch0_ue_count'
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This attribute file will display the count of UEs on this
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DIMM located in channel 0.
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Channel 0 DIMM Label control file:
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'ch0_dimm_label'
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This control file allows this DIMM to have a label assigned
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to it. With this label in the module, when errors occur
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the output can provide the DIMM label in the system log.
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This becomes vital for panic events to isolate the
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cause of the UE event.
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DIMM Labels must be assigned after booting, with information
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that correctly identifies the physical slot with its
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silk screen label. This information is currently very
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motherboard specific and determination of this information
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must occur in userland at this time.
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Channel 1 CE Count attribute file:
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'ch1_ce_count'
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This attribute file will display the count of CEs on this
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DIMM located in channel 1.
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Channel 1 UE Count attribute file:
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'ch1_ue_count'
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This attribute file will display the count of UEs on this
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DIMM located in channel 0.
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Channel 1 DIMM Label control file:
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'ch1_dimm_label'
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This control file allows this DIMM to have a label assigned
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to it. With this label in the module, when errors occur
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the output can provide the DIMM label in the system log.
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This becomes vital for panic events to isolate the
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cause of the UE event.
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DIMM Labels must be assigned after booting, with information
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that correctly identifies the physical slot with its
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silk screen label. This information is currently very
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motherboard specific and determination of this information
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must occur in userland at this time.
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============================================================================
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SYSTEM LOGGING
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If logging for UEs and CEs are enabled then system logs will have
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error notices indicating errors that have been detected:
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MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0,
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channel 1 "DIMM_B1": amd76x_edac
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MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0,
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channel 1 "DIMM_B1": amd76x_edac
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The structure of the message is:
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the memory controller (MC0)
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Error type (CE)
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memory page (0x283)
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offset in the page (0xce0)
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the byte granularity (grain 8)
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or resolution of the error
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the error syndrome (0xb741)
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memory row (row 0)
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memory channel (channel 1)
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DIMM label, if set prior (DIMM B1
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and then an optional, driver-specific message that may
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have additional information.
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Both UEs and CEs with no info will lack all but memory controller,
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error type, a notice of "no info" and then an optional,
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driver-specific error message.
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============================================================================
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PCI Bus Parity Detection
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On Header Type 00 devices the primary status is looked at
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for any parity error regardless of whether Parity is enabled on the
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device. (The spec indicates parity is generated in some cases).
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On Header Type 01 bridges, the secondary status register is also
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looked at to see if parity occurred on the bus on the other side of
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the bridge.
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SYSFS CONFIGURATION
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Under /sys/devices/system/edac/pci are control and attribute files as follows:
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Enable/Disable PCI Parity checking control file:
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'check_pci_parity'
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This control file enables or disables the PCI Bus Parity scanning
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operation. Writing a 1 to this file enables the scanning. Writing
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a 0 to this file disables the scanning.
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Enable:
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echo "1" >/sys/devices/system/edac/pci/check_pci_parity
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Disable:
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echo "0" >/sys/devices/system/edac/pci/check_pci_parity
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Panic on PCI PARITY Error:
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'panic_on_pci_parity'
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This control files enables or disables panicking when a parity
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error has been detected.
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module/kernel parameter: panic_on_pci_parity=[0|1]
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Enable:
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echo "1" >/sys/devices/system/edac/pci/panic_on_pci_parity
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Disable:
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echo "0" >/sys/devices/system/edac/pci/panic_on_pci_parity
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Parity Count:
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'pci_parity_count'
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This attribute file will display the number of parity errors that
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have been detected.
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PCI Device Whitelist:
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'pci_parity_whitelist'
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This control file allows for an explicit list of PCI devices to be
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scanned for parity errors. Only devices found on this list will
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be examined. The list is a line of hexadecimal VENDOR and DEVICE
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ID tuples:
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1022:7450,1434:16a6
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One or more can be inserted, separated by a comma.
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To write the above list doing the following as one command line:
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echo "1022:7450,1434:16a6"
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> /sys/devices/system/edac/pci/pci_parity_whitelist
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To display what the whitelist is, simply 'cat' the same file.
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PCI Device Blacklist:
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'pci_parity_blacklist'
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This control file allows for a list of PCI devices to be
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skipped for scanning.
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The list is a line of hexadecimal VENDOR and DEVICE ID tuples:
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1022:7450,1434:16a6
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One or more can be inserted, separated by a comma.
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To write the above list doing the following as one command line:
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echo "1022:7450,1434:16a6"
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> /sys/devices/system/edac/pci/pci_parity_blacklist
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To display what the whitelist currently contains,
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simply 'cat' the same file.
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=======================================================================
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PCI Vendor and Devices IDs can be obtained with the lspci command. Using
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the -n option lspci will display the vendor and device IDs. The system
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administrator will have to determine which devices should be scanned or
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skipped.
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The two lists (white and black) are prioritized. blacklist is the lower
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priority and will NOT be utilized when a whitelist has been set.
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Turn OFF a whitelist by an empty echo command:
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echo > /sys/devices/system/edac/pci/pci_parity_whitelist
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and any previous blacklist will be utilized.
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