linux-kernel - Re: [PATCH v1 2/2] perf header: Support hybrid CPU_PMU

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Message-ID: <YJFjTCsk9dCd6QP7@krava>
Date:   Tue, 4 May 2021 17:07:56 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v1 2/2] perf header: Support hybrid CPU_PMU_CAPS

On Fri, Apr 30, 2021 at 03:46:02PM +0800, Jin Yao wrote:
> On hybrid platform, it may have several cpu pmus, such as,
> "cpu_core" and "cpu_atom". The CPU_PMU_CAPS feature in perf
> header needs to be improved to support multiple cpu pmus.
> 
> The new layout in header is defined as:
> 
> <nr_caps>
> <caps string>
> <caps string>
> <pmu name>
> <nr of rest pmus>

not sure why is the 'nr of rest pmus' needed

the current format is:

        u32 nr_cpu_pmu_caps;
        {
                char    name[];
                char    value[];
        } [nr_cpu_pmu_caps]


I guess we could extend it to:

        u32 nr_cpu_pmu_caps;
        {
                char    name[];
                char    value[];
        } [nr_cpu_pmu_caps]
	char pmu_name[]

        u32 nr_cpu_pmu_caps;
        {
                char    name[];
                char    value[];
        } [nr_cpu_pmu_caps]
	char pmu_name[]

	...

and we could detect the old format by checking that there's no
pmu name.. but maybe I'm missing something, I did not check deeply,
please let me know

also would be great to move the format change and storing hybrid
pmus in separate patches

thanks,
jirka