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SubjectRe: [PATCH v4 2/6] perf record: Get the first sample time and last sample time
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On 10/20/2017 4:25 AM, Arnaldo Carvalho de Melo wrote:
> Em Thu, Oct 19, 2017 at 05:21:27PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Tue, Oct 03, 2017 at 10:22:34PM +0800, Jin Yao escreveu:
>>> In perf record, it's walked on all samples yet. So it's very easy to get
>>
>> You're saying that perf record walks all samples always? That only
>> happens when we generate the build-id table, right? And people disable
>> that to speed up the process, knowing that some limitations will come
>> from that, for doing analysis right after running it is mostly OK to
>> disable the build-id processing.
>
> So either you add a new option that processes all events without doing
> build-id processing (and all the locking, struct thread, map, etc
> processing it entails) and just looks at the sample->time, and when
> build id processing is enabled, just do as you're doing in this patch,
> then, at perf report --time you should look to see if those start/end
> times were filled in and if not tell that to the user, i.e. that
> either --record-time-boundaries (or a better name :-) ) has to be used,
> or, that build-id process, with a short explanation that
> --record-time-boundaries is a bit cheaper.
>
> - Arnaldo
>

Hi Arnaldo,

Thanks so much for reminding me that the walking only happens when
build-id processing is enabled. Yes, the step is same as what you said
so there will be an issue when the build-id processing is disabled.

According to your suggestion, I will provide a new option
"--record-time-boundaries" in perf record. If user disables the build-id
processing, the perf record will ask user to set the
"--record-time-boundaries". If user enables the build-id processing, the
perf record will not ask user to set the "--record-time-boundaries".

Also in perf report, if it doesn't see start/end time filled in the perf
file header, it will show some information to let user know he should
set "--record-time-boundaries" or enable the build-id processing in perf
record.

I will provide v5 patch series, maybe some days later.

Thanks
Jin Yao





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