c5905afb0e
So here's a boot tested patch on top of Jason's series that does
all the cleanups I talked about and turns jump labels into a
more intuitive to use facility. It should also address the
various misconceptions and confusions that surround jump labels.
Typical usage scenarios:
#include <linux/static_key.h>
struct static_key key = STATIC_KEY_INIT_TRUE;
if (static_key_false(&key))
do unlikely code
else
do likely code
Or:
if (static_key_true(&key))
do likely code
else
do unlikely code
The static key is modified via:
static_key_slow_inc(&key);
...
static_key_slow_dec(&key);
The 'slow' prefix makes it abundantly clear that this is an
expensive operation.
I've updated all in-kernel code to use this everywhere. Note
that I (intentionally) have not pushed through the rename
blindly through to the lowest levels: the actual jump-label
patching arch facility should be named like that, so we want to
decouple jump labels from the static-key facility a bit.
On non-jump-label enabled architectures static keys default to
likely()/unlikely() branches.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: a.p.zijlstra@chello.nl
Cc: mathieu.desnoyers@efficios.com
Cc: davem@davemloft.net
Cc: ddaney.cavm@gmail.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>
214 lines
5.9 KiB
Plaintext
214 lines
5.9 KiB
Plaintext
#
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# General architecture dependent options
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#
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config OPROFILE
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tristate "OProfile system profiling"
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depends on PROFILING
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depends on HAVE_OPROFILE
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select RING_BUFFER
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select RING_BUFFER_ALLOW_SWAP
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help
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OProfile is a profiling system capable of profiling the
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whole system, include the kernel, kernel modules, libraries,
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and applications.
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If unsure, say N.
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config OPROFILE_EVENT_MULTIPLEX
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bool "OProfile multiplexing support (EXPERIMENTAL)"
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default n
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depends on OPROFILE && X86
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help
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The number of hardware counters is limited. The multiplexing
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feature enables OProfile to gather more events than counters
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are provided by the hardware. This is realized by switching
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between events at an user specified time interval.
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If unsure, say N.
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config HAVE_OPROFILE
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bool
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config OPROFILE_NMI_TIMER
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def_bool y
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depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI
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config KPROBES
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bool "Kprobes"
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depends on MODULES
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depends on HAVE_KPROBES
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select KALLSYMS
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help
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Kprobes allows you to trap at almost any kernel address and
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execute a callback function. register_kprobe() establishes
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a probepoint and specifies the callback. Kprobes is useful
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for kernel debugging, non-intrusive instrumentation and testing.
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If in doubt, say "N".
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config JUMP_LABEL
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bool "Optimize very unlikely/likely branches"
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depends on HAVE_ARCH_JUMP_LABEL
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help
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This option enables a transparent branch optimization that
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makes certain almost-always-true or almost-always-false branch
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conditions even cheaper to execute within the kernel.
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Certain performance-sensitive kernel code, such as trace points,
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scheduler functionality, networking code and KVM have such
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branches and include support for this optimization technique.
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If it is detected that the compiler has support for "asm goto",
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the kernel will compile such branches with just a nop
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instruction. When the condition flag is toggled to true, the
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nop will be converted to a jump instruction to execute the
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conditional block of instructions.
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This technique lowers overhead and stress on the branch prediction
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of the processor and generally makes the kernel faster. The update
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of the condition is slower, but those are always very rare.
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( On 32-bit x86, the necessary options added to the compiler
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flags may increase the size of the kernel slightly. )
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config OPTPROBES
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def_bool y
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depends on KPROBES && HAVE_OPTPROBES
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depends on !PREEMPT
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config HAVE_EFFICIENT_UNALIGNED_ACCESS
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bool
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help
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Some architectures are unable to perform unaligned accesses
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without the use of get_unaligned/put_unaligned. Others are
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unable to perform such accesses efficiently (e.g. trap on
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unaligned access and require fixing it up in the exception
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handler.)
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This symbol should be selected by an architecture if it can
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perform unaligned accesses efficiently to allow different
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code paths to be selected for these cases. Some network
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drivers, for example, could opt to not fix up alignment
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problems with received packets if doing so would not help
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much.
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See Documentation/unaligned-memory-access.txt for more
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information on the topic of unaligned memory accesses.
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config HAVE_SYSCALL_WRAPPERS
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bool
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config KRETPROBES
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def_bool y
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depends on KPROBES && HAVE_KRETPROBES
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config USER_RETURN_NOTIFIER
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bool
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depends on HAVE_USER_RETURN_NOTIFIER
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help
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Provide a kernel-internal notification when a cpu is about to
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switch to user mode.
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config HAVE_IOREMAP_PROT
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bool
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config HAVE_KPROBES
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bool
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config HAVE_KRETPROBES
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bool
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config HAVE_OPTPROBES
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bool
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#
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# An arch should select this if it provides all these things:
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#
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# task_pt_regs() in asm/processor.h or asm/ptrace.h
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# arch_has_single_step() if there is hardware single-step support
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# arch_has_block_step() if there is hardware block-step support
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# asm/syscall.h supplying asm-generic/syscall.h interface
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# linux/regset.h user_regset interfaces
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# CORE_DUMP_USE_REGSET #define'd in linux/elf.h
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# TIF_SYSCALL_TRACE calls tracehook_report_syscall_{entry,exit}
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# TIF_NOTIFY_RESUME calls tracehook_notify_resume()
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# signal delivery calls tracehook_signal_handler()
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#
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config HAVE_ARCH_TRACEHOOK
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bool
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config HAVE_DMA_ATTRS
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bool
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config USE_GENERIC_SMP_HELPERS
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bool
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config HAVE_REGS_AND_STACK_ACCESS_API
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bool
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help
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This symbol should be selected by an architecure if it supports
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the API needed to access registers and stack entries from pt_regs,
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declared in asm/ptrace.h
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For example the kprobes-based event tracer needs this API.
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config HAVE_CLK
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bool
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help
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The <linux/clk.h> calls support software clock gating and
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thus are a key power management tool on many systems.
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config HAVE_DMA_API_DEBUG
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bool
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config HAVE_HW_BREAKPOINT
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bool
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depends on PERF_EVENTS
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config HAVE_MIXED_BREAKPOINTS_REGS
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bool
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depends on HAVE_HW_BREAKPOINT
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help
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Depending on the arch implementation of hardware breakpoints,
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some of them have separate registers for data and instruction
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breakpoints addresses, others have mixed registers to store
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them but define the access type in a control register.
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Select this option if your arch implements breakpoints under the
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latter fashion.
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config HAVE_USER_RETURN_NOTIFIER
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bool
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config HAVE_PERF_EVENTS_NMI
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bool
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help
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System hardware can generate an NMI using the perf event
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subsystem. Also has support for calculating CPU cycle events
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to determine how many clock cycles in a given period.
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config HAVE_ARCH_JUMP_LABEL
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bool
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config HAVE_ARCH_MUTEX_CPU_RELAX
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bool
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config HAVE_RCU_TABLE_FREE
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bool
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config ARCH_HAVE_NMI_SAFE_CMPXCHG
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bool
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config HAVE_ALIGNED_STRUCT_PAGE
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bool
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help
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This makes sure that struct pages are double word aligned and that
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e.g. the SLUB allocator can perform double word atomic operations
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on a struct page for better performance. However selecting this
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might increase the size of a struct page by a word.
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config HAVE_CMPXCHG_LOCAL
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bool
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config HAVE_CMPXCHG_DOUBLE
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bool
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source "kernel/gcov/Kconfig"
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