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From: Frederic Weisbecker on 12 Jun 2010 03:40
Hi,

In this new version, the weird hangs have been fixed. They were
due to some ACTIVE state checks that didn't handle the paused
mode.

And also comes a new pmu->reserve callback to schedule an event
on the cpu without actually starting it (as if ->stop() was
just called in it).
In x86 it is the same than the enable() callback, the decision
to activate the event beeing eventually handled by checking the
PERF_EVENT_STATE_PAUSED. On software events it is a stub as
they can be activated anytime in a lightweight fashion, without
the need to fight against a finite resource.

BTW, there is a quite handy way to make a diff between task
context and task + irq context profiling.

Just run:

sudo ./perf stat -r 10 -e task-clock -e task-clock:t -e cs -e cs:t \
-e migrations -e migrations:t -e faults -e faults:t -e cycles \
-e cycles:t -e instructions -e instructions:t -e branches \
-e branches:t -e branch-misses -e branch-misses:t taskset 1 hackbench 1

(Did I just say handy?)

Example of result:

Performance counter stats for 'taskset 1 hackbench 1' (10 runs):

604,727182 task-clock-msecs # 0,969 CPUs ( +- 6,176% )
604,727182 task-clock-msecs # 0,969 CPUs ( +- 6,176% )
11584 context-switches # 0,019 M/sec ( +- 26,945% )
11593 context-switches # 0,019 M/sec ( +- 26,909% )
1 CPU-migrations # 0,000 M/sec ( +- 61,464% )
0 CPU-migrations # 0,000 M/sec ( +- 100,000% )
1844 page-faults # 0,003 M/sec ( +- 1,425% )
1847 page-faults # 0,003 M/sec ( +- 1,423% )
917442262 cycles # 1517,118 M/sec ( +- 6,814% ) (scaled from 69,40%)
908980892 cycles # 1503,126 M/sec ( +- 5,807% ) (scaled from 68,51%)
335812687 instructions # 0,368 IPC ( +- 6,977% ) (scaled from 73,77%)
321284628 instructions # 0,352 IPC ( +- 6,377% ) (scaled from 20,59%)
48956776 branches # 80,957 M/sec ( +- 5,936% ) (scaled from 22,67%)
48144741 branches # 79,614 M/sec ( +- 6,480% ) (scaled from 21,68%)
2310259 branch-misses # 4,758 % ( +- 9,698% ) (scaled from 15,11%)
2200507 branch-misses # 4,532 % ( +- 9,294% ) (scaled from 15,35%)

0,624082951 seconds time elapsed ( +- 5,939% )


Most of the time, the instruction counter diff shows that irqs take 0.01% of noise
with hackbench. Something that does more IO would probably be a more
interesting example.

The thing is pullable there:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
perf/exclusion-4

Thanks.


Frederic Weisbecker (5):
perf: Provide a proper stop action for software events
perf: Support disable() after stop() on software events
perf: Ability to enable in a paused mode
perf: Introduce task, softirq and hardirq contexts exclusion
perf: Support for task/softirq/hardirq exclusion on tools

arch/x86/kernel/cpu/perf_event.c | 7 +-
include/linux/perf_event.h | 52 ++++++++-
kernel/hw_breakpoint.c | 1 +
kernel/perf_event.c | 257 +++++++++++++++++++++++++++++++-------
kernel/softirq.c | 6 +
kernel/trace/trace_event_perf.c | 2 +-
tools/perf/util/parse-events.c | 37 ++++--
7 files changed, 302 insertions(+), 60 deletions(-)

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