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Subject: Re: [PATCH 6/9] perf report: Support instruction latency
From:   Athira Rajeev <atrajeev@linux.vnet.ibm.com>
In-Reply-To: <2f2ede9e-b098-4921-59e2-1289bdc87ba1@linux.intel.com>
Date:   Sun, 7 Feb 2021 22:15:00 +0530
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>, mingo@kernel.org,
        linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>, eranian@google.com,
        namhyung@kernel.org, jolsa@redhat.com, ak@linux.intel.com,
        yao.jin@linux.intel.com, maddy@linux.vnet.ibm.com
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References: <1612296553-21962-1-git-send-email-kan.liang@linux.intel.com>
 <1612296553-21962-7-git-send-email-kan.liang@linux.intel.com>
 <A90940CE-3DFB-4774-BA46-0C5FEB4953A0@linux.vnet.ibm.com>
 <27633871-eda5-7faa-8783-84dd49f8a6cd@linux.intel.com>
 <6F377E9D-89F8-414F-A2CC-C96797697159@linux.vnet.ibm.com>
 <2f2ede9e-b098-4921-59e2-1289bdc87ba1@linux.intel.com>
To:     "Liang, Kan" <kan.liang@linux.intel.com>
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> On 05-Feb-2021, at 8:21 PM, Liang, Kan <kan.liang@linux.intel.com> =
wrote:
>=20
>=20
>=20
> On 2/5/2021 7:55 AM, Athira Rajeev wrote:
>>>> Because in other archs, the var2_w of =E2=80=98perf_sample_weight=E2=80=
=99 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.
>>>=20
>>> 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
>=20
> Yes, I don't think PowerPC should force var2_w to data->ins_lat. I =
think you can create your own field.
>=20
>> as you mentioned. I checked the below patch defining an =
=E2=80=98arch_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  =
=E2=80=98arch_perf_parse_sample_weight', it will report =E2=80=98Local =
Weight=E2=80=99 wrongly since weak function takes it as 64 bit. Not sure =
if that is a valid case to consider though.
>=20
> 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@l=
inux.intel.com/
>=20
> 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.=20

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.=20
The default setting for powerpc works with out breaking anything and =
verified using =E2=80=9Cperf mem record <workload>=E2=80=9D

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

Thanks
Athira Rajeev
>=20
> Thanks,
> Kan