linux-kernel - Re: [Patch v1 04/10] perf/x86: add memory profiling via PEBS Load Latency

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Date:	Mon, 29 Oct 2012 16:43:04 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [Patch v1 04/10] perf/x86: add memory profiling via PEBS Load Latency

On Mon, Oct 29, 2012 at 4:38 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2012-10-29 at 16:15 +0100, Stephane Eranian wrote:
>> +       fll = event->hw.flags & PERF_X86_EVENT_PEBS_LDLAT;
>> +
>>         perf_sample_data_init(&data, 0, event->hw.last_period);
>>
>> +       data.period = event->hw.last_period;
>> +       sample_type = event->attr.sample_type;
>> +
>> +       /*
>> +        * if PEBS-LL or PreciseStore
>> +        */
>> +       if (fll) {
>> +               if (sample_type & PERF_SAMPLE_ADDR)
>> +                       data.addr = pebs->dla;
>> +
>> +               /*
>> +                * Use latency for cost (only avail with PEBS-LL)
>> +                */
>> +               if (fll && (sample_type & PERF_SAMPLE_COST))
>> +                       data.cost = pebs->lat;
>> +
>> +               /*
>> +                * data.dsrc encodes the data source
>> +                */
>> +               if (sample_type & PERF_SAMPLE_DSRC) {
>> +                       if (fll)
>> +                               data.dsrc.val = load_latency_data(pebs->dse);
>> +               }
>> +       }
>
>
> Why does fl1 exist? the above looks really convoluted, all fl1 checks
> inside are pointless. Also 'fl1' is a bizarre name, 'pebs_ll' would be a
> better name I guess.
>
You meant fll, instead I think.

> What's wrong with:
>
>         if (event->hw.flags & PERF_X86_EVENT_PEBS_LDLAT) {
>                 if (sample_type & PERF_SAMPLE_ADDR)
>                         data.addr = pebs->dla;
>
>                 if (sample_type & PERF_SAMPLE_COST)
>                         data.cost = perf->lat;
>
>                 if (sample_type & PERF_SAMPLE_DSRC)
>                         data.dsrc.val = load_latency_data(pebs->dse);
>         }
>
Well, that would work too, but I am trying to factorize the code
with Precise Store which is a later patch. But we could clone
your proposal and do:

>         if (event->hw.flags & PERF_X86_EVENT_PEBS_ST) {
>                 if (sample_type & PERF_SAMPLE_ADDR)
>                         data.addr = pebs->dla;
>
>                 if (sample_type & PERF_SAMPLE_DSRC)
>                         data.dsrc.val = precise_store_data(pebs->dse);
>         }

I am fine with that too.
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