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Date:   Mon, 21 Oct 2019 12:27:06 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
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>,
        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 1/4] perf/core,x86: introduce sync_task_ctx() method
 at struct pmu
Message-ID: <20191021102706.GE1800@hirez.programming.kicks-ass.net>
References: <0b20a07f-d074-d3da-7551-c9a4a94fe8e3@linux.intel.com>
 <c75134ef-b71b-c080-8ee1-c09fb9fae764@linux.intel.com>
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On Fri, Oct 18, 2019 at 12:42:44PM +0300, Alexey Budankov wrote:
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 61448c19a132..60bf17af69f0 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -409,6 +409,13 @@ struct pmu {
>  	 */
>  	size_t				task_ctx_size;
>  
> +	/*
> +	 * PMU specific parts of task perf event context (i.e. ctx->task_ctx_data)
> +	 * can be synchronized using this function. See Intel LBR callstack support
> +	 * implementation and Perf core context switch handling callbacks for usage
> +	 * examples.

You're forgetting to mark this: Optional

> +	 */

> +	void (*sync_task_ctx)		(void *one, void *another);

The traditional argment names for context switching functions are prev
and next.