linux-kernel - Re: [RFC/PATCH 1/2] perf top: Fix -z option behavior

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Message-ID: <87d2bxc8r0.fsf@sejong.aot.lge.com>
Date:	Tue, 19 Aug 2014 15:07:47 +0900
From:	Namhyung Kim <namhyung@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Namhyung Kim <namhyung.kim@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>
Subject: Re: [RFC/PATCH 1/2] perf top: Fix -z option behavior

On Wed, 13 Aug 2014 17:27:56 -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Aug 12, 2014 at 05:16:05PM +0900, Namhyung Kim escreveu:
>> The current -z option does almost nothing.  It doesn't zero the
>> existing samples so that we can see profiles of exited process after
>> last refresh.  It seems it only affects annotation.
>> 
>> This patch clears existing entries before processing if -z option is
>> given.  For this original decaying logic also moved before processing.
>
> So, this is two things bolted into one, i.e. it is not stated here why
> decaying needs to be done before resorting. I bet its because since
> we're zeroing everything, no need to decay anything, right?

Exactly.

>
> Stating more clearly what is the intent and the reason for changes helps
> reviewing.

Yep, will do better next time.

>
> Anyway, will add a note about that and apply the change.

Thank you!

>
> Also, the delete entries thing could zero total stats in struct hists,
> which is not a problem currently, because, IIRC, the collapse/resort
> logic will do that when it rotates the hists, but if we ever want to
> just delete events and then add a bunch of events without resorting, we
> will end up with bogus stats that will have the sum of the old events
> stats with the new ones.

Right.  I'll send the fix.

Thanks,
Namhyung
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