linux-kernel - Re: [tip:perf/urgent] perf/x86/intel/pt: Generate PMI in the STOP region as well

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Date:	Tue, 17 May 2016 10:40:34 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	stable@...r.kernel.org, gregkh@...uxfoundation.org,
	jolsa@...hat.com, tglx@...utronix.de,
	torvalds@...ux-foundation.org, vincent.weaver@...ne.edu,
	bp@...en8.de, hpa@...or.com, eranian@...gle.com,
	markus.t.metzger@...el.com, acme@...hat.com,
	linux-kernel@...r.kernel.org, acme@...radead.org,
	peterz@...radead.org
Subject: Re: [tip:perf/urgent] perf/x86/intel/pt: Generate PMI in the STOP
 region as well


* Alexander Shishkin <alexander.shishkin@...ux.intel.com> wrote:

> tip-bot for Alexander Shishkin <tipbot@...or.com> writes:
> 
> > Commit-ID:  ab92b232ae05c382c3df0e3d6a5c6d16b639ac8c
> > Gitweb:     http://git.kernel.org/tip/ab92b232ae05c382c3df0e3d6a5c6d16b639ac8c
> > Author:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > AuthorDate: Tue, 10 May 2016 16:18:32 +0300
> > Committer:  Ingo Molnar <mingo@...nel.org>
> > CommitDate: Thu, 12 May 2016 14:45:59 +0200
> >
> > perf/x86/intel/pt: Generate PMI in the STOP region as well
> >
> > Currently, the PT driver always sets the PMI bit one region (page) before
> > the STOP region so that we can wake up the consumer before we run out of
> > room in the buffer and have to disable the event. However, we also need
> > an interrupt in the last output region, so that we actually get to disable
> > the event (if no more room from new data is available at that point),
> > otherwise hardware just quietly refuses to start, but the event is
> > scheduled in and we end up losing trace data till the event gets removed.
> >
> > For a cpu-wide event it is even worse since there may not be any
> > re-scheduling at all and no chance for the ring buffer code to notice
> > that its buffer is filled up and the event needs to be disabled (so that
> > the consumer can re-enable it when it finishes reading the data out). In
> > other words, all the trace data will be lost after the buffer gets filled
> > up.
> >
> > This patch makes PT also generate a PMI when the last output region is
> > full.
> >
> > Reported-by: Markus Metzger <markus.t.metzger@...el.com>
> > Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Cc: <stable@...r.kernel.org>
> 
> Can we also have this one queued up for stable 4.4 and 4.5?

Agreed.

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo