linux-kernel - Re: [PATCH V9 8/8] perf tools: handle PERF_RECORD_LOST

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Date:	Tue, 12 May 2015 14:43:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	"Liang, Kan" <kan.liang@...el.com>, Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 8/8] perf tools: handle PERF_RECORD_LOST_SAMPLES

On Mon, May 11, 2015 at 06:27:58PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, May 11, 2015 at 08:40:56PM +0000, Liang, Kan escreveu:
> > > Em Sun, May 10, 2015 at 03:13:15PM -0400, Kan Liang escreveu:
> > > > $ perf record -e '{cycles:p,instructions:p}' -c 20003 --no-time
> > > > ~/tchain ~/tchain [perf record: Woken up 148 times to write data]
> > > > [perf record: Captured and wrote 36.922 MB perf.data (1206322
> > > > samples)]
> 
> > > > $ perf report -D | tail
> > > >           SAMPLE events:     120243
> > > >            MMAP2 events:          5
> > > >     LOST_SAMPLES events:         24
> > > >   FINISHED_ROUND events:         15
> > > > cycles:p stats:
> > > >            TOTAL events:      59348
> > > >           SAMPLE events:      59348
> > > > instructions:p stats:
> > > >            TOTAL events:      60895
> > > >           SAMPLE events:      60895
> 
> > > The example doesn't show which of cycles:p or instructions:p got lost, isn't
> > > that possible? Guess not from the patch, but should, no? I.e. what is
> > > PERF_SAMPLE_ID for then?
>  
> > Yes, it's possible to know the lost samples number for cycles:p or
> > instructions:p. But I didn't implement it in the summary of perf report -D.
> > I think a total lost_samples number is enough for user. What they really
> > care about should be the total samples drop rate. 
> > (If they really want to know the number of which event got lost, they can
> > search LOST_SAMPLES in perf report -D. sample->id is dumped with lost
> > number.) 
> 
> I disagree, since the support is there, we need to have it in
> hists->events_stats[PERF_RECORD_LOST_SAMPLES].
> 
> But that can be done in a follow up patch.

Agreed, it would be good to know of which event the samples got lost.

> It just came quickly to my attention because of all the discussion about
> where to store something (PERF_SAMPLE_ID via sample_type + sample_id_all)
> that doesn't get used in the patch that introduces it :-)
> 
> I'll try to test this all tomorrow and will try to do the needed wiring
> to hists_evsel->hists->events_stats.
> 
> All working I can push this all via my perf/core event, if PeterZ
> agrees and is ok with the kernel specific bits.

I would like to carry these as there some conflicts with other patches I
have.
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