linux-kernel - Re: [PATCH 2/2] perf, tools, stat: Reset ids counter when retrying events

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Message-ID: <20180221143337.GC24416@kernel.org>
Date:   Wed, 21 Feb 2018 11:33:37 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <andi@...stfloor.org>, jolsa@...nel.org,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] perf, tools, stat: Reset ids counter when retrying
 events

Em Wed, Feb 21, 2018 at 03:31:17PM +0100, Jiri Olsa escreveu:
> On Thu, Oct 05, 2017 at 07:00:29PM -0700, Andi Kleen wrote:
> > From: Andi Kleen <ak@...ux.intel.com>
> 
> ouch, sry for overlooking this
> 
> > 
> > perf stat can retry opening events. After opening an file descriptor
> > it adds the ids to the ecsel. Each event keeps a running
> > count of ids. When we decide to close an evsel and retry
> > with a different configuration this count needs to be reset,
> > otherwise it can overflow the buffer.
> 
> how can this happen? we call store_counter_ids at the
> end of the loop, when the evsel is all done and can't
> be reconfigured

Yeah, I couldn't figure out the exact sequence, but I think that we need
to reset those hash tables when doing a perf_evlist__close(), no? I.e.
when we open we may get new ids, so need to rehash?

- Arnaldo