linux-kernel - Re: [PATCH 6/9] perf report: Support instruction latency

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Date:   Sun, 7 Feb 2021 22:15:00 +0530
From:   Athira Rajeev <atrajeev@...ux.vnet.ibm.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>, mingo@...nel.org,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>, eranian@...gle.com,
        namhyung@...nel.org, jolsa@...hat.com, ak@...ux.intel.com,
        yao.jin@...ux.intel.com, maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH 6/9] perf report: Support instruction latency



> On 05-Feb-2021, at 8:21 PM, Liang, Kan <kan.liang@...ux.intel.com> wrote:
> 
> 
> 
> On 2/5/2021 7:55 AM, Athira Rajeev wrote:
>>>> Because in other archs, the var2_w of ‘perf_sample_weight’ could be used to capture something else than the Local INSTR Latency.
>>>> Can we have some weak function to populate the header string ?
>>> I agree that the var2_w has different meanings among architectures. We should not force it to data->ins_lat.
>>> 
>>> The patch as below should fix it. Does it work for you?
>> My point about weak function was actually for the arch specific header string. But I guess we should not force it to data->ins_lat
> 
> Yes, I don't think PowerPC should force var2_w to data->ins_lat. I think you can create your own field.
> 
>> as you mentioned. I checked the below patch defining an ‘arch_perf_parse_sample_weight' for powerpc and it works.
>> But one observation is that, for cases with kernel having support for PERF_SAMPLE_WEIGHT_STRUCT but missing arch specific support for  ‘arch_perf_parse_sample_weight', it will report ‘Local Weight’ wrongly since weak function takes it as 64 bit. Not sure if that is a valid case to consider though.
> 
> Currently, the PERF_SAMPLE_WEIGHT_STRUCT is only enabled on X86 by default.
> https://lore.kernel.org/lkml/1612296553-21962-6-git-send-email-kan.liang@linux.intel.com/
> 
> For PowerPC, the PERF_SAMPLE_WEIGHT is still the default setting. There is no way to set PERF_SAMPLE_WEIGHT_STRUCT via perf tool.
> I don't think the above case will happen.

Yes. 

I tested with kernel changes from perf/core branch of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
And perf tools side changes from tmp.perf/core branch of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git along with the above change. 
The default setting for powerpc works with out breaking anything and verified using “perf mem record <workload>”

Tested-by: Athira Rajeev <atrajeev@...ux.vnet.ibm.com>

Thanks
Athira Rajeev
> 
> Thanks,
> Kan