From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>,
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>,
Kan Liang <kan.liang@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 v3 4/4] perf/core,x86: synchronize PMU task contexts on optimized context switches
Date: Mon, 21 Oct 2019 12:37:45 +0200 [thread overview]
Message-ID: <20191021103745.GF1800@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20191021075942.GA8809@gmail.com>
On Mon, Oct 21, 2019 at 09:59:42AM +0200, Ingo Molnar wrote:
>
> * Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
>
> > + /*
> > + * PMU specific parts of task perf context may require
> > + * additional synchronization, at least for proper Intel
> > + * LBR callstack data profiling;
> > + */
> > + pmu->sync_task_ctx(ctx->task_ctx_data,
> > + next_ctx->task_ctx_data);
>
> Firstly, I'm pretty sure you never run this on a CPU where
> pmu->sync_task_ctx is NULL, right? ;-)
>
> Secondly, even on Intel CPUs in many cases we'll just call into a ~2 deep
> function pointer based call hierarchy, just to find that nothing needs to
See prototype here for getting rid of at least one layer of indirect
calls:
https://lkml.kernel.org/r/20191007083831.26880701.6@infradead.org
> be done, because there's no LBR call stack maintained:
>
> + if (!one || !another)
> + return;
>
> So while it's technically a layering violation, it might make sense to
> elevate this check to the generic layer and say that synchronization
> calls by the core layer will always provide two valid pointers?
Alternatively we can write the thing like:
if (pmu->swap_task_ctx)
pmu->swap_task_ctx(ctx, next_ctx)
else
swap(ctx->task_ctx_data, next_ctx->task_ctx_data);
next prev parent reply other threads:[~2019-10-21 10:37 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-18 9:17 [PATCH v3 0/4]: perf/core: fix restoring of Intel LBR call stack on a context switch Alexey Budankov
2019-10-18 9:42 ` [PATCH v3 1/4] perf/core,x86: introduce sync_task_ctx() method at struct pmu Alexey Budankov
2019-10-21 10:27 ` Peter Zijlstra
2019-10-21 11:24 ` Alexey Budankov
2019-10-18 9:43 ` [PATCH v3 2/4] perf/x86: install platform specific sync_task_ctx adapter Alexey Budankov
2019-10-18 9:44 ` [PATCH v3 3/4] perf/x86/intel: implement LBR callstacks context synchronization Alexey Budankov
2019-10-18 9:45 ` [PATCH v3 4/4] perf/core,x86: synchronize PMU task contexts on optimized context switches Alexey Budankov
2019-10-21 7:59 ` Ingo Molnar
2019-10-21 10:00 ` Alexey Budankov
2019-10-21 10:37 ` Peter Zijlstra [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-10-16 14:20 [PATCH v3 0/4]: perf/core: fix restoring of Intel LBR call stack on a context switch Alexey Budankov
2019-10-16 14:28 ` [PATCH v3 4/4] perf/core,x86: synchronize PMU task contexts on optimized context switches Alexey Budankov
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