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perf/core, pt, bts: Get rid of itrace_started

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I just noticed that hw.itrace_started and hw.config are aliased to the
same location. Now, the PT driver happens to use both, which works out
fine by sheer luck:

 - STORE(hw.itrace_start) is ordered before STORE(hw.config), in the
    program order, although there are no compiler barriers to ensure that,

 - to the perf_log_itrace_start() hw.itrace_start looks set at the same
   time as when it is intended to be set because both stores happen in the
   same path,

 - hw.config is never reset to zero in the PT driver.

Now, the use of hw.config by the PT driver makes more sense (it being a
HW PMU) than messing around with itrace_started, which is an awkward API
to begin with.

This patch replaces hw.itrace_started with an attach_state bit and an
API call for the PMU drivers to use to communicate the condition.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20170330153956.25994-1-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Alexander Shishkin
2017-03-30 18:39:56 +03:00
committed by Ingo Molnar
parent e0563e0495
commit 8d4e6c4caa
4 changed files with 12 additions and 7 deletions
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7
kernel/events/core.c
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@@ -7301,6 +7301,11 @@ static void perf_log_throttle(struct perf_event *event, int enable)
perf_output_end(&handle);
}
void perf_event_itrace_started(struct perf_event *event)
{
event->attach_state |= PERF_ATTACH_ITRACE;
}
static void perf_log_itrace_start(struct perf_event *event)
{
struct perf_output_handle handle;
@@ -7316,7 +7321,7 @@ static void perf_log_itrace_start(struct perf_event *event)
event = event->parent;
if (!(event->pmu->capabilities & PERF_PMU_CAP_ITRACE) ||
event->hw.itrace_started)
event->attach_state & PERF_ATTACH_ITRACE)
return;
rec.header.type = PERF_RECORD_ITRACE_START;