linux-kernel - [BUG] perf: perf_output

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Message-ID: <CABPqkBQa8ndydqkMDvc3kzu84_96FbK77TUkrfO3eSPXmv3dhQ@mail.gmail.com>
Date:	Wed, 13 Jun 2012 14:51:03 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...e.hu
Subject: [BUG] perf: perf_output_sample() merge issue?

Peter,

I was looking at perf_output_sample() today, when I ran
into the following weird statement coming from:

commit a7ac67ea021b4603095d2aa458bc41641238f22c
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date:   Mon Jun 27 16:47:16 2011 +0200

    perf: Remove the perf_output_begin(.sample) argument

    Since only samples call perf_output_sample() its much saner (and more

I think the intent of this commit was to add the watermark check
at the very end of the perf_output_sample() and NOT between processing
of RAW and BRANCH_STACK. Something may have gone wrong
in the merge.

Can you confirm this?

perf_output_sample()
{
        if (sample_type & PERF_SAMPLE_RAW) {
        }

        if (!event->attr.watermark) {
                int wakeup_events = event->attr.wakeup_events;

                if (wakeup_events) {
                        struct ring_buffer *rb = handle->rb;
                        int events = local_inc_return(&rb->events);

                        if (events >= wakeup_events) {
                                local_sub(wakeup_events, &rb->events);
                                local_inc(&rb->wakeup);
                        }
                }
        }

        if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
        }
}
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