linux-kernel - Re: [V5 PATCH] perf parse-events: Specially handle uncore event alias in small groups

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Message-ID: <20180501163340.GB11539@krava>
Date:   Tue, 1 May 2018 18:33:40 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, namhyung@...nel.org,
        ganapatrao.kulkarni@...ium.com, zhangshaokun@...ilicon.com,
        yao.jin@...ux.intel.com, will.deacon@....com, ak@...ux.intel.com,
        agustinv@...eaurora.org
Subject: Re: [V5 PATCH] perf parse-events: Specially handle uncore event
 alias in small groups

On Tue, May 01, 2018 at 07:31:36AM -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> Perf stat doesn't count the uncore event aliases from the same uncore
> block in a group, for example:
> 
>   perf stat -e '{unc_m_cas_count.all,unc_m_clockticks}' -a -I 1000
>   #           time             counts unit events
>        1.000447342      <not counted>      unc_m_cas_count.all
>        1.000447342      <not counted>      unc_m_clockticks
>        2.000740654      <not counted>      unc_m_cas_count.all
>        2.000740654      <not counted>      unc_m_clockticks
> 
> The output is very misleading. It gives a wrong impression that the
> uncore event doesn't work.
> 
> An uncore block could be composed by several PMUs. An uncore event alias
> is a joint name which means the same event runs on all PMUs of a block.
> Perf doesn't support mixed events from different PMUs in the same group.
> It is wrong to put uncore event aliases in a big group.
> 
> The right way is to split the big group into multiple small groups which
> only include the events from the same PMU.
> Only uncore event aliases from the same uncore block should be specially
> handled here. It doesn't make sense to mix the uncore events with other
> uncore events from different blocks or even core events in a group.
> 
> With the patch:
>   #           time             counts unit events
>      1.001557653            140,833      unc_m_cas_count.all
>      1.001557653      1,330,231,332      unc_m_clockticks
>      2.002709483             85,007      unc_m_cas_count.all
>      2.002709483      1,429,494,563      unc_m_clockticks
> 
> Reported-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> ---
> 
> Changes since V4:
> - Add WARN_ON when failing to alloc an array for leaders
> - Add comments to explain why it has to go through the whole group

Acked-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka