From: Alexey Budankov <alexey.budankov@linux.intel.com>
To: "Liang, Kan" <kan.liang@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Andi Kleen <ak@linux.intel.com>,
Stephane Eranian <eranian@google.com>,
Ian Rogers <irogers@google.com>, Song Liu <songliubraving@fb.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/4] perf/x86/intel: implement LBR callstacks context synchronization
Date: Wed, 16 Oct 2019 17:07:05 +0300 [thread overview]
Message-ID: <c39bc36c-b1eb-f9b4-edbb-47de3b1f32ca@linux.intel.com> (raw)
In-Reply-To: <b40cfea3-6df4-f7ea-b47a-c0ccf8a241f4@linux.intel.com>
On 16.10.2019 16:39, Alexey Budankov wrote:
> On 16.10.2019 15:20, Liang, Kan wrote:
>>
>>
>> On 10/16/2019 5:50 AM, Alexey Budankov wrote:
>>>
>>> Implement intel_pmu_lbr_sync_task_ctx() method that updates counter
>>> of the events that requested LBR callstack data on a sample.
>>>
>>> The counter can be zero for the case when task context belongs to
>>> a thread that has just come from a block on a futex and the context
>>> contains saved (lbr_stack_state == LBR_VALID) LBR register values.
>>>
>>> For the values to be restored at LBR registers on the next thread's
>>> switch-in event it copies the counter value that is expected to be
>>> non zero from the previous equivalent task perf event context.
>>>
>>> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
>>> ---
>>> arch/x86/events/intel/lbr.c | 9 +++++++++
>>> arch/x86/events/perf_event.h | 3 +++
>>> 2 files changed, 12 insertions(+)
>>>
>>> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
>>> index ea54634eabf3..152a3f8b516a 100644
>>> --- a/arch/x86/events/intel/lbr.c
>>> +++ b/arch/x86/events/intel/lbr.c
>>> @@ -417,6 +417,15 @@ static void __intel_pmu_lbr_save(struct x86_perf_task_context *task_ctx)
>>> cpuc->last_log_id = ++task_ctx->log_id;
>>> }
>>> +void intel_pmu_lbr_sync_task_ctx(struct x86_perf_task_context *one,
>>> + struct x86_perf_task_context *another)
>>> +{
>>> + if (!one || !another)
>>> + return;
>>> +
>>> + one->lbr_callstack_users = another->lbr_callstack_users;
>>
>> We may want to swap here?
>
> Well, in this particular case lbr_callstack_users has to stay consistent
> with the amount of events in task perf event context that requested
> LBR callstack.
Tested swap version and it also fixes the initial issue.
After more code revising swap looks like the correct operation here.
Nice catch. Thanks!
~Alexey
>
> ~Alexey
>
>>
>> Thanks,
>> Kan
>>
>>> +}
>>> +
>>> void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in)
>>> {
>>> struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
>>> diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
>>> index a25e6d7eb87b..3e0087c06fc9 100644
>>> --- a/arch/x86/events/perf_event.h
>>> +++ b/arch/x86/events/perf_event.h
>>> @@ -1024,6 +1024,9 @@ void intel_pmu_store_pebs_lbrs(struct pebs_lbr *lbr);
>>> void intel_ds_init(void);
>>> +void intel_pmu_lbr_sync_task_ctx(struct x86_perf_task_context *one,
>>> + struct x86_perf_task_context *another);
>>> +
>>> void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in);
>>> u64 lbr_from_signext_quirk_wr(u64 val);
>>>
>>
>
next prev parent reply other threads:[~2019-10-16 14:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 9:41 [PATCH v2 0/4]: perf/core: fix restoring of Intel LBR call stack on a context switch Alexey Budankov
2019-10-16 9:48 ` [PATCH v2 1/4] perf/core,x86: introduce sync_task_ctx() method at struct pmu Alexey Budankov
2019-10-16 9:49 ` [PATCH v2 2/4] perf/x86: install platform specific sync_task_ctx adapter Alexey Budankov
2019-10-16 9:50 ` [PATCH v2 3/4] perf/x86/intel: implement LBR callstacks context synchronization Alexey Budankov
2019-10-16 12:20 ` Liang, Kan
2019-10-16 13:39 ` Alexey Budankov
2019-10-16 14:07 ` Alexey Budankov [this message]
2019-10-16 9:51 ` [PATCH v2 4/4] perf/core,x86: synchronize PMU task contexts on optimized context switches Alexey Budankov
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