linux-kernel - Re: [RFC PATCH v3 00/14] Share events between metrics

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Date:   Fri, 8 May 2020 17:12:38 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        John Garry <john.garry@...wei.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Kim Phillips <kim.phillips@....com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC PATCH v3 00/14] Share events between metrics

On Thu, May 07, 2020 at 10:36:15PM -0700, Ian Rogers wrote:
> Metric groups contain metrics. Metrics create groups of events to
> ideally be scheduled together. Often metrics refer to the same events,
> for example, a cache hit and cache miss rate. Using separate event
> groups means these metrics are multiplexed at different times and the
> counts don't sum to 100%. More multiplexing also decreases the
> accuracy of the measurement.
> 
> This change orders metrics from groups or the command line, so that
> the ones with the most events are set up first. Later metrics see if
> groups already provide their events, and reuse them if
> possible. Unnecessary events and groups are eliminated.

Yes some improvements here are great.

> 
> The option --metric-no-group is added so that metrics aren't placed in
> groups. This affects multiplexing and may increase sharing.
> 
> The option --metric-mo-merge is added and with this option the
> existing grouping behavior is preserved.

Could we also make this a per metric option, like

-M foo:nomerge,... 

or somesuch? Okay i suppose this could be a followon.

Ultimatively like you said we probably want to configure
defaults in the event file.

-Andi