linux-kernel - Re: [PATCH v2] perf evsel: Don't set sample_regs_intr/sample_regs

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Message-ID: <20200804120616.GD3440834@kernel.org>
Date:   Tue, 4 Aug 2020 09:06:16 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     "Jin, Yao" <yao.jin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>,
        jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        irogers@...gle.com
Subject: Re: [PATCH v2] perf evsel: Don't set
 sample_regs_intr/sample_regs_user for dummy event

Em Tue, Aug 04, 2020 at 10:06:56AM +0300, Adrian Hunter escreveu:
> On 29/07/20 10:23 am, Jin, Yao wrote:
> > Hi Adrian,
> > 
> > Could you help to check if following condition will break PT?
> > 
> > "(opts->sample_intr_regs && !evsel->no_aux_samples &&
> > !evsel__is_dummy_event(evsel))"
> 
> Sorry for slow response - I've been away.
> 
> This is fine.  It will not break PT.
> 
> no_aux_samples is useful for evsels that have been added by the code rather
> than requested by the user.  For old kernels PT adds sched_switch tracepoint
> to track context switches (before the current context switch event was
> added) and having auxiliary sample information unnecessarily uses up space
> in the perf buffer.
> 
> Acked-by: Adrian Hunter <adrian.hunter@...el.com>

Thanks for checking and providing the comment, that I added as a
committer note together with your Acked-by, appreciated.

- Arnaldo