linux-kernel - Re: metric expressions including metrics?

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Date:   Mon, 18 May 2020 21:20:51 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Paul A. Clarke" <pc@...ibm.com>
Cc:     Ian Rogers <irogers@...gle.com>,
        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>,
        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>,
        Andi Kleen <ak@...ux.intel.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>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Leo Yan <leo.yan@...aro.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: metric expressions including metrics?

On Mon, May 18, 2020 at 02:12:42PM -0500, Paul A. Clarke wrote:
> I'm curious how hard it would be to define metrics using other metrics,
> in the metrics definition files.
> 
> Currently, to my understanding, every metric definition must be an
> expresssion based solely on arithmetic combinations of hardware events.
> 
> Some metrics are hierarchical in nature such that a higher-level metric
> can be defined as an arithmetic expression of two other metrics, e.g.
> 
> cache_miss_cycles_per_instruction =
>   data_cache_miss_cycles_per_instruction +
>   instruction_cache_miss_cycles_per_instruction
> 
> This would need to be defined something like:
> dcache_miss_cpi = "dcache_miss_cycles / instructions"
> icache_miss_cpi = "icache_miss_cycles / instructions"
> cache_miss_cpi = "(dcache_miss_cycles + icache_miss_cycles) / instructions"
> 
> Could the latter definition be simplified to:
> cache_miss_cpi = "dcache_miss_cpi + icache_miss_cpi"
> 
> With multi-level caches and NUMA hierarchies, some of these higher-level
> metrics can involve a lot of hardware events.
> 
> Given the recent activity in this area, I'm curious if this has been
> considered and already on a wish/to-do list, or found onerous.

hi,
actually we were discussing this with Ian and Stephane and I plan on
checking on that.. should be doable, I'll keep you in the loop

jirka

> 
> Regards,
> Paul Clarke
>