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From:   Stephane Eranian <eranian@google.com>
Date:   Fri, 15 Jun 2018 09:54:44 -0700
Message-ID: <CABPqkBRgDSVCyg_qF3dYLpE+9cO0Woria+Jk+BdOA_6_VCYQfw@mail.gmail.com>
Subject: Re: [PATCH v1 0/2] perf: Drop leaked kernel samples
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     yao.jin@linux.intel.com,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        me@kylehuey.com, LKML <Linux-kernel@vger.kernel.org>,
        Vince Weaver <vincent.weaver@maine.edu>,
        Will Deacon <will.deacon@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        "Liang, Kan" <kan.liang@intel.com>, "Jin, Yao" <yao.jin@intel.com>
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Hi,
On Fri, Jun 15, 2018 at 1:12 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, Jun 15, 2018 at 04:01:45PM +0800, Jin, Yao wrote:
>
> > Bring more overhead to kernel if we zero the bits considering the number of
> > leaked samples may be not too small?
>
> Keeping the samples at least allows you to know how many samples
> happened and such things.
>
Yes, important point. You cannot just drop a sample. It may break some
calculations
done like num_samples x fixed_periods = total number of events observed. Some
tools do this.


> > And the skid information may be interesting (see example of hitting on
> > page_fault in previous mail). If we zero it, we will not know.
>
> If you throw them out the window you also don't know, do you?