linux-kernel - Re: [RFC PATCH v3 12/14] perf metricgroup: order event groups by size

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Date:   Fri, 8 May 2020 19:40:19 -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>,
        LKML <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC PATCH v3 12/14] perf metricgroup: order event groups by size

> > I'm not sure if size is that great an heuristic. The dedup algorithm should
> > work in any case even if you don't order by size, right?
> 
> Consider two metrics:
>  - metric 1 with events {A,B}
>  - metric 2 with events {A,B,C,D}
> If the list isn't sorted then as the matching takes the first group
> with all the events, metric 1 will match {A,B} and metric 2 {A,B,C,D}.
> If the order is sorted to {A,B,C,D},{A,B} then metric 1 matches within
> the {A,B,C,D} group as does metric 2. The events in metric 1 aren't
> used and are removed.

Ok. It's better for the longer metric if they stay together.

> 
> The dedup algorithm is very naive :-)

I guess what matters is that it gives reasonable results on the current
metrics. I assume it does?

How much deduping is happening if you run all metrics?

For toplev on my long term todo list was to compare it against
a hopefully better schedule generated by or-tools, but I never
got around to coding that up.

-Andi