Re: [PING] [PATCH] Preheat CPU in benchtests

[OndÅej BÃlka <neleai at seznam dot cz>]

On Wed, May 01, 2013 at 09:23:47PM +0200, OndÅej BÃlka wrote:
> 
> Ping, 
> 
> I need something like this for following patches. This is better than
> nothing until environment setting utility is implemented.
> 
> OK to commit?
>
And as now multiple variants are in a first one will be three times
slower just because it went slower without this patch.
 
> On Tue, Apr 23, 2013 at 08:10:28AM +0200, OndÅej BÃlka wrote:
> > Hi, 
> > 
> > Benchmarks now are affected by cpu scaling when initialy run at low
> > frequency.
> > 
> > Following benchmark runs nonsensial loop first to ensure that benchmark
> > are measured at maximal frequency. This greatly cuts time needed to
> > get accurate results.
> > 
> 
> ---
>  benchtests/bench-skeleton.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/benchtests/bench-skeleton.c b/benchtests/bench-skeleton.c
> index 7359184..2c728bf 100644
> --- a/benchtests/bench-skeleton.c
> +++ b/benchtests/bench-skeleton.c
> @@ -22,6 +22,8 @@
>  #include <time.h>
>  #include <inttypes.h>
>  
> +volatile double dontoptimize = 0.0;
> +
>  #define TIMESPEC_AFTER(a, b) \
>    (((a).tv_sec == (b).tv_sec) ?						      \
>       ((a).tv_nsec > (b).tv_nsec) :					      \
> @@ -32,6 +34,13 @@ main (int argc, char **argv)
>    unsigned long i, k;
>    struct timespec start, end, runtime;
>  
> +  /* This loop should cause CPU switch to maximal freqency.  This makes
> +      subsequent measurement more accurate.  We need side effect to avoid loop
> +      being deleted by compiler.  */
> + for(k = 0; k < 1000000; k++)
> +   dontoptimize += 23.0 * dontoptimize + 2.1;
> +
> +
>    memset (&runtime, 0, sizeof (runtime));
>    memset (&start, 0, sizeof (start));
>    memset (&end, 0, sizeof (end));
> -- 
> 1.7.4.4

-- 

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