Impact: New perf_counter features
This primarily adds a way for perf_counter users to enable and disable
counters and groups. Enabling or disabling a counter or group also
enables or disables all of the child counters that have been cloned
from it to monitor children of the task monitored by the top-level
counter. The userspace interface to enable/disable counters is via
ioctl on the counter file descriptor.
Along the way this extends the code that handles child counters to
handle child counter groups properly. A group with multiple counters
will be cloned to child tasks if and only if the group leader has the
hw_event.inherit bit set - if it is set the whole group is cloned as a
group in the child task.
In order to be able to enable or disable all child counters of a given
top-level counter, we need a way to find them all. Hence I have added
a child_list field to struct perf_counter, which is the head of the
list of children for a top-level counter, or the link in that list for
a child counter. That list is protected by the perf_counter.mutex
field.
This also adds a mutex to the perf_counter_context struct. Previously
the list of counters was protected just by the lock field in the
context, which meant that perf_counter_init_task had to take that lock
and then take whatever lock/mutex protects the top-level counter's
child_list. But the counter enable/disable functions need to take
that lock in order to traverse the list, then for each counter take
the lock in that counter's context in order to change the counter's
state safely, which will lead to a deadlock.
To solve this, we now have both a mutex and a spinlock in the context,
and taking either is sufficient to ensure the list of counters can't
change - you have to take both before changing the list. Now
perf_counter_init_task takes the mutex instead of the lock (which
incidentally means that inherit_counter can use GFP_KERNEL instead of
GFP_ATOMIC) and thus avoids the possible deadlock. Similarly the new
enable/disable functions can take the mutex while traversing the list
of child counters without incurring a possible deadlock when the
counter manipulation code locks the context for a child counter.
We also had an misfeature that the first counter added to a context
would possibly not go on until the next sched-in, because we were
using ctx->nr_active to detect if the context was running on a CPU.
But nr_active is the number of active counters, and if that was zero
(because the context didn't have any counters yet) it would look like
the context wasn't running on a cpu and so the retry code in
__perf_install_in_context wouldn't retry. So this adds an 'is_active'
field that is set when the context is on a CPU, even if it has no
counters. The is_active field is only used for task contexts, not for
per-cpu contexts.
If we enable a subsidiary counter in a group that is active on a CPU,
and the arch code can't enable the counter, then we have to pull the
whole group off the CPU. We do this with group_sched_out, which gets
moved up in the file so it comes before all its callers. This also
adds similar logic to __perf_install_in_context so that the "all on,
or none" invariant of groups is preserved when adding a new counter to
a group.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: New perf_counter features
A pinned counter group is one that the user wants to have on the CPU
whenever possible, i.e. whenever the associated task is running, for
a per-task group, or always for a per-cpu group. If the system
cannot satisfy that, it puts the group into an error state where
it is not scheduled any more and reads from it return EOF (i.e. 0
bytes read). The group can be released from error state and made
readable again using prctl(PR_TASK_PERF_COUNTERS_ENABLE). When we
have finer-grained enable/disable controls on counters we'll be able
to reset the error state on individual groups.
An exclusive group is one that the user wants to be the only group
using the CPU performance monitor hardware whenever it is on. The
counter group scheduler will not schedule an exclusive group if there
are already other groups on the CPU and will not schedule other groups
onto the CPU if there is an exclusive group scheduled (that statement
does not apply to groups containing only software counters, which can
always go on and which do not prevent an exclusive group from going on).
With an exclusive group, we will be able to let users program PMU
registers at a low level without the concern that those settings will
perturb other measurements.
Along the way this reorganizes things a little:
- is_software_counter() is moved to perf_counter.h.
- cpuctx->active_oncpu now records the number of hardware counters on
the CPU, i.e. it now excludes software counters. Nothing was reading
cpuctx->active_oncpu before, so this change is harmless.
- A new cpuctx->exclusive field records whether we currently have an
exclusive group on the CPU.
- counter_sched_out moves higher up in perf_counter.c and gets called
from __perf_counter_remove_from_context and __perf_counter_exit_task,
where we used to have essentially the same code.
- __perf_counter_sched_in now goes through the counter list twice, doing
the pinned counters in the first loop and the non-pinned counters in
the second loop, in order to give the pinned counters the best chance
to be scheduled in.
Note that only a group leader can be exclusive or pinned, and that
attribute applies to the whole group. This avoids some awkwardness in
some corner cases (e.g. where a group leader is closed and the other
group members get added to the context list). If we want to relax that
restriction later, we can, and it is easier to relax a restriction than
to apply a new one.
This doesn't yet handle the case where a pinned counter is inherited
and goes into error state in the child - the error state is not
propagated up to the parent when the child exits, and arguably it
should.
Signed-off-by: Paul Mackerras <paulus@samba.org>
This makes sure that we call the platform-specific ppc_md.enable_pmcs
function on each CPU before we try to use the PMU on that CPU. If the
CPU goes off-line and then on-line, we need to do the enable_pmcs call
again, so we use the hw_perf_counter_setup hook to ensure that. It gets
called as each CPU comes online, but it isn't called on the CPU that is
coming up, so this adds the CPU number as an argument to it (there were
no non-empty instances of hw_perf_counter_setup before).
This also arranges to set the pmcregs_in_use field of the lppaca (data
structure shared with the hypervisor) on each CPU when we are using the
PMU and clear it when we are not. This allows the hypervisor to optimize
partition switches by not saving/restoring the PMU registers when we
aren't using the PMU.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Software counters aren't subject to the limitations imposed by the
fixed number of hardware counter registers, so there is no reason not
to enable them all in __perf_counter_sched_in. Previously we used to
break out of the loop when we got to a group that wouldn't fit on the
PMU; with this we continue through the list but only schedule in
software counters (or groups containing only software counters) from
there on.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: minimize requirements on architectures
Currently, an architecture just enabling CONFIG_PERF_COUNTERS but not
providing any extra functions will fail to build with
perf_counter_print_debug being undefined, since we don't provide an
empty dummy definition like we do with the hw_perf_* functions.
This provides an empty dummy perf_counter_print_debug() to make it
easier for architectures to turn on CONFIG_PERF_COUNTERS.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: extend perf_counter infrastructure
This adds an optional hw_perf_group_sched_in() arch function that enables
a whole group of counters in one go. It returns 1 if it added the group
successfully, 0 if it did nothing (and therefore the core needs to add
the counters individually), or a negative number if an error occurred.
It should add all the counters and enable any software counters in the
group, or else add none of them and return an error.
There are a couple of related changes/improvements in the group handling
here:
* As an optimization, group_sched_out() and group_sched_in() now check the
state of the group leader, and do nothing if the leader is not active
or disabled.
* We now call hw_perf_save_disable/hw_perf_restore around the complete
set of counter enable/disable calls in __perf_counter_sched_in/out,
to give the arch code the opportunity to defer updating the hardware
state until the hw_perf_restore call if it wants.
* We no longer stop adding groups after we get to a group that has more
than one counter. We will ultimately add an option for a group to be
exclusive. The current code doesn't really implement exclusive groups
anyway, since a group could end up going on with other counters that
get added before it.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: bug fix
Currently if you do (e.g.) timec -e -1 ls, it will report 0 for the
value of the cpu_clock counter. The reason is that the core assumes
that a counter's count field is up-to-date when the counter is inactive,
and doesn't call the counter's read function. However, the cpu_clock
counter code only updates the count in the read function.
This fixes it by making both the read and disable functions update the
count. It also makes the counter ignore time passing while the counter
is disabled, by making the enable function update the hw.prev_count field.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: fix oops-causing bug
Currently, if you try to use perf_counters on an architecture that has
no hardware support, and you select an event that doesn't map to any of
the defined software counters, you get an oops rather than an error.
This is because the dummy hw_perf_counter_init returns ERR_PTR(-EINVAL)
but the caller (perf_counter_alloc) only tests for NULL.
This makes the dummy hw_perf_counter_init return NULL instead.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Impact: fix panic possible panic
Some versions of GCC inline the weak global function if it's empty.
Add a barrier() to work it around.
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: clean up and refactor code
refactor the counter scheduler: separate out in/out functions and
introduce a counter-rotation function as well.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: remove dead code
nr_inherited was not maintained correctly (not decremented) - and also
not used - remove it.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Allow lowlevel ->enable() op to return an error if a counter can not be
added. This can be used to handle counter constraints.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: schedule in groups atomically
If there are multiple groups in a task, make sure they are scheduled
in and out atomically.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: implement default-off counters
Make sure that counters that are created with counter.hw_event.disabled=1,
get created in disabled state.
They can be enabled via:
prctl(PR_TASK_PERF_COUNTERS_ENABLE);
Signed-off-by: Ingo Molnar <mingo@elte.hu>
If counters are exiting via do_exit() not via filp close, then
the CPU context needs to be released - otherwise future percpu
counter creations might fail.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new feature, new sw counter
Add a counter that counts the number of pagefaults a task
is experiencing.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new feature, new sw counter
Add a counter that counts the number of cross-CPU migrations a
task is suffering.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new feature, new sw counter
Add a counter that counts the number of context-switches a task
is doing.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: implement new performance feature
Counter inheritance can be used to run performance counters in a workload,
transparently - and pipe back the counter results to the parent counter.
Inheritance for performance counters works the following way: when creating
a counter it can be marked with the .inherit=1 flag. Such counters are then
'inherited' by all child tasks (be they fork()-ed or clone()-ed). These
counters get inherited through exec() boundaries as well (except through
setuid boundaries).
The counter values get added back to the parent counter(s) when the child
task(s) exit - much like stime/utime statistics are gathered. So inherited
counters are ideal to gather summary statistics about an application's
behavior via shell commands, without having to modify that application.
The timec.c command utilizes counter inheritance:
http://redhat.com/~mingo/perfcounters/timec.c
Sample output:
$ ./timec -e 1 -e 3 -e 5 ls -lR /usr/include/ >/dev/null
Performance counter stats for 'ls':
163516953 instructions
2295 cache-misses
2855182 branch-misses
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: restructure code
Change counter math from absolute values to clear delta logic.
We try to extract elapsed deltas from the raw hw counter - and put
that into the generic counter.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: cleanup
Introduce a proper enum for the 3 states of a counter:
PERF_COUNTER_STATE_OFF = -1
PERF_COUNTER_STATE_INACTIVE = 0
PERF_COUNTER_STATE_ACTIVE = 1
and rename counter->active to counter->state and propagate the
changes everywhere.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Add a way for self-monitoring tasks to disable/enable counters summarily,
via a prctl:
PR_TASK_PERF_COUNTERS_DISABLE 31
PR_TASK_PERF_COUNTERS_ENABLE 32
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new perf-counter type
The 'task clock' counter counts the amount of time a task is executing,
in nanoseconds. It stops ticking when a task is scheduled out either due
to it blocking, sleeping or it being preempted.
This counter type is a Linux kernel based abstraction, it is available
even if the hardware does not support native hardware performance counters.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: cleanup
Rename them to better match up the usual IRQ disable/enable APIs:
hw_perf_disable_all() => hw_perf_save_disable()
hw_perf_restore_ctrl() => hw_perf_restore()
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add new perf-counter type
The 'CPU clock' counter counts the amount of CPU clock time that is
elapsing, in nanoseconds. (regardless of how much of it the task is
spending on a CPU executing)
This counter type is a Linux kernel based abstraction, it is available
even if the hardware does not support native hardware performance counters.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: restructure code, introduce hw_ops driver abstraction
Introduce this abstraction to handle counter details:
struct hw_perf_counter_ops {
void (*hw_perf_counter_enable) (struct perf_counter *counter);
void (*hw_perf_counter_disable) (struct perf_counter *counter);
void (*hw_perf_counter_read) (struct perf_counter *counter);
};
This will be useful to support assymetric hw details, and it will also
be useful to implement "software counters". (Counters that count kernel
managed sw events such as pagefaults, context-switches, wall-clock time
or task-local time.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: bugfix
Check that a group does not span outside the context of a CPU or a task.
Also, do not allow deep recursive hierarchies.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: add group counters
This patch adds the "counter groups" abstraction.
Groups of counters behave much like normal 'single' counters, with a
few semantic and behavioral extensions on top of that.
A counter group is created by creating a new counter with the open()
syscall's group-leader group_fd file descriptor parameter pointing
to another, already existing counter.
Groups of counters are scheduled in and out in one atomic group, and
they are also roundrobin-scheduled atomically.
Counters that are member of a group can also record events with an
(atomic) extended timestamp that extends to all members of the group,
if the record type is set to PERF_RECORD_GROUP.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: clean up new API
Thorough cleanup of the new perf counters API, we now get clean separation
of the various concepts:
- introduce perf_counter_hw_event to separate out the event source details
- move special type flags into separate attributes: PERF_COUNT_NMI,
PERF_COUNT_RAW
- extend the type to u64 and reserve it fully to the architecture in the
raw type case.
And make use of all these changes in the core and x86 perfcounters code.
Also change the syscall signature to:
asmlinkage int sys_perf_counter_open(
struct perf_counter_hw_event *hw_event_uptr __user,
pid_t pid,
int cpu,
int group_fd);
( Note that group_fd is unused for now - it's reserved for the counter
groups abstraction. )
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: change syscall, cleanup
Make use of the new perf_counters event type.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Implement the core kernel bits of Performance Counters subsystem.
The Linux Performance Counter subsystem provides an abstraction of
performance counter hardware capabilities. It provides per task and per
CPU counters, and it provides event capabilities on top of those.
Performance counters are accessed via special file descriptors.
There's one file descriptor per virtual counter used.
The special file descriptor is opened via the perf_counter_open()
system call:
int
perf_counter_open(u32 hw_event_type,
u32 hw_event_period,
u32 record_type,
pid_t pid,
int cpu);
The syscall returns the new fd. The fd can be used via the normal
VFS system calls: read() can be used to read the counter, fcntl()
can be used to set the blocking mode, etc.
Multiple counters can be kept open at a time, and the counters
can be poll()ed.
See more details in Documentation/perf-counters.txt.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
