Latency = weigth in perf mem record/report?

Latency = weigth in perf mem record/report?

[Harald Servat]

Dear list,

   table 18-18 from the Vol 3b part 2 of the Intel® 64 and IA-32 
Architectures  Software Developer’s Manual (labeled as Table 18-18. PEBS 
Record Format for Intel Core i7 Processor Family ) [1] indicates that 
the PEBS samples report the latency value (in core cycles) for that 
particular load/store that emitted the sample at the address 0xa8 from 
the begin of the PEBS sample address.

   I've seen that there is a weight field in the output of the perf 
report -D associated to the PERF_RECORD_SAMPLE. Looking at the kernel 
code I found in file arch/x86/kernel/cpu/perf_event_intel_ds.c the 
following code which seems to be storing the info I want

  819         /*
  820          * Use latency for weight (only avail with PEBS-LL)
  821          */
  822         if (fll && (sample_type & PERF_SAMPLE_WEIGHT))
  823             data.weight = pebs->lat;

   and then in tools/perf/builtin-mem.c the routine dump_raw_samples 
seems to dump this info. Am I right? Can anyone kindly confirm this?

Thank you very much.

[1] 
http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3b-part-2-manual.pdf

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Re: Latency = weigth in perf mem record/report?

[Jiri Olsa]

On Thu, Feb 13, 2014 at 06:08:43PM +0100, Harald Servat wrote:
> Dear list,
> 
>   table 18-18 from the Vol 3b part 2 of the Intel® 64 and IA-32
> Architectures  Software Developer’s Manual (labeled as Table 18-18.
> PEBS Record Format for Intel Core i7 Processor Family ) [1]
> indicates that the PEBS samples report the latency value (in core
> cycles) for that particular load/store that emitted the sample at
> the address 0xa8 from the begin of the PEBS sample address.
> 
>   I've seen that there is a weight field in the output of the perf
> report -D associated to the PERF_RECORD_SAMPLE. Looking at the
> kernel code I found in file
> arch/x86/kernel/cpu/perf_event_intel_ds.c the following code which
> seems to be storing the info I want
> 
>  819         /*
>  820          * Use latency for weight (only avail with PEBS-LL)
>  821          */
>  822         if (fll && (sample_type & PERF_SAMPLE_WEIGHT))
>  823             data.weight = pebs->lat;
> 
>   and then in tools/perf/builtin-mem.c the routine dump_raw_samples
> seems to dump this info. Am I right? Can anyone kindly confirm this?

Right, PEBS latency info is stored in sample's WEIGHT (for mem-loads and
mem-stores events), and it's sample->weight on the perf tool side.

jirka