Re: [PATCH 17/19] perf tools: Always force PERF_RECORD_FINISHED_ROUND event

From: Arnaldo Carvalho de Melo
Date: Fri Jul 25 2014 - 10:14:22 EST

Em Fri, Jul 25, 2014 at 01:34:26PM +0200, Jiri Olsa escreveu:
> On Thu, Jul 24, 2014 at 06:34:51PM -0300, Arnaldo Carvalho de Melo wrote:
> > I think both changes are OK, but should be split in different patches,

> right, I'll split it


> > [root@zoo /]# perf stat -r 5 perf report --no-ordered-samples > /dev/null
> > 101,171,572,553 instructions # 1.10 insns per cycle
> > 30.249514999 seconds time elapsed ( +- 0.48% )

> > [root@zoo /]# perf stat -r 5 perf report --ordered-samples > /dev/null
> > 105,982,144,263 instructions # 1.04 insns per cycle
> > 32.636483981 seconds time elapsed ( +- 0.41% )

> so those 2 extra seconds is the ordering time, right? sounds ok

Yeah, but I think its worth investigating if using it is a strict
requirement in all cases, i.e. is it possible to receive out of order
events when sampling on a single CPU? Or a single CPU socket with a
coherent time source? etc.

Providing a way to disable this ordering to be used in corner cases
where it is not a strict requirement and the volume of samples is so
high that reducing processing time like shown above seems to be a
sensible thing to do.

We're in the business of optimizing stuff, huh? :-)

- Arnaldo
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