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

Stephane Eranian
2012-10-29T15:43:07Z

On Mon, Oct 29, 2012 at 4:38 PM, Peter Zijlstra <peterz@infradead.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.