linux-kernel - Re: [PATCH 10/10] perf tests: Use lower sample

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Date:	Tue, 12 Nov 2013 11:41:01 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 10/10] perf tests: Use lower sample_freq in sw clock
 event period test

Em Tue, Nov 12, 2013 at 09:07:36AM +0200, Adrian Hunter escreveu:
> On 11/11/13 22:22, Arnaldo Carvalho de Melo wrote:
> > We were using it at 10 kHz, which doesn't work in machines where somehow
> > the max freq was auto reduced by the kernel:
> >
> > [root@...andy ~]# perf test 19
> > 19: Test software clock events have valid period values    : FAILED!
> > [root@...andy ~]# perf test -v 19
> > 19: Test software clock events have valid period values    :
> > --- start ---
> > Couldn't open evlist: Invalid argument
> > ---- end ----
> > Test software clock events have valid period values: FAILED!
> > [root@...andy ~]#
> >
> > [root@...andy ~]# cat /proc/sys/kernel/perf_event_max_sample_rate
> > 7000
> >
> > Reducing it to 500 Hz should be good enough for this test and also
> > shouldn't affect what it is testing.
> >
> > But warn the user if it fails, informing the knob and the freq tried.
> 
> Doesn't work for me:
> 
> ./perf test -v 19
> 19: Test software clock events have valid period values    :
> --- start ---
> mmap size 528384B
> mmap size 528384B
> All (0) samples have period value of 1!
> ---- end ----
> Test software clock events have valid period values: FAILED!
> 
> But this fixes it:
> 
> diff --git a/tools/perf/tests/sw-clock.c b/tools/perf/tests/sw-clock.c
> index 93a7139..6664a7c 100644
> --- a/tools/perf/tests/sw-clock.c
> +++ b/tools/perf/tests/sw-clock.c
> @@ -9,7 +9,7 @@
>  #include "util/cpumap.h"
>  #include "util/thread_map.h"
>  
> -#define NR_LOOPS  1000000
> +#define NR_LOOPS  10000000

Lower frequency, need to generate more noise, ugh. Adding that, but I
think this test needs to be reworked, Namhyung?

- Arnaldo
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