Re: V2 [PATCH] benchtests: Restore the clock_gettime option

[Carlos O'Donell <carlos@redhat.com>]

On 5/20/20 2:14 PM, H.J. Lu via Libc-alpha wrote:
> On Wed, May 20, 2020 at 11:05 AM Florian Weimer <fweimer@redhat.com> wrote:
>>
>> * Alexander Monakov via Libc-alpha:
>>
>>> I am well aware. Again: rdtsc does not count CPU cycles on recent
>>> Intel CPUs.
>>
>> H.J. probably has a different view on what those “recent Intel CPUs”
>> are. 8-) I have not reviewed the mechanics of the patch, but if we need
>> this for some CPUs, we should make the change.
>>
> 
> Here the patch with updated commit message:
> 
> commit 7621e38bf3c58b2d0359545f1f2898017fd89d05
> Author: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Date:   Tue Jan 29 17:43:45 2019 +0000
> 
>     Add generic hp-timing support
> 
> removed the clock_gettime option.  Restore the clock_gettime option for
> some x86 CPUs on which value from RDTSC may not be incremented at a fixed
> rate.
> 
> OK for master?

OK for master. 

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
 
> Thanks.
> 
> From 7e48f7adbd53c18df7ab5fdd488bfcc134627480 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Mon, 18 May 2020 17:28:42 -0700
> Subject: [PATCH] benchtests: Restore the clock_gettime option
> 
> commit 7621e38bf3c58b2d0359545f1f2898017fd89d05
> Author: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Date:   Tue Jan 29 17:43:45 2019 +0000
> 
>     Add generic hp-timing support
> 
> removed the clock_gettime option.  Restore the clock_gettime option for
> some x86 CPUs on which value from RDTSC may not be incremented at a fixed
> rate.
> ---
>  benchtests/Makefile       | 6 ++++++
>  benchtests/README         | 7 ++++++-
>  benchtests/bench-timing.h | 6 +++++-
>  3 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/benchtests/Makefile b/benchtests/Makefile
> index 335d643ecb..99e90d17a0 100644
> --- a/benchtests/Makefile
> +++ b/benchtests/Makefile
> @@ -132,11 +132,17 @@ endif
>  
>  CPPFLAGS-nonlib += -DDURATION=$(BENCH_DURATION) -D_ISOMAC
>  
> +# Use clock_gettime to measure performance of functions.  The default is
> +# to use the architecture-specific high precision timing instructions.
> +ifdef USE_CLOCK_GETTIME
> +CPPFLAGS-nonlib += -DUSE_CLOCK_GETTIME
> +else
>  # On x86 processors, use RDTSCP, instead of RDTSC, to measure performance
>  # of functions.  All x86 processors since 2010 support RDTSCP instruction.
>  ifdef USE_RDTSCP
>  CPPFLAGS-nonlib += -DUSE_RDTSCP
>  endif
> +endif
>  
>  DETAILED_OPT :=
>  
> diff --git a/benchtests/README b/benchtests/README
> index c4f03fd872..f440f3295a 100644
> --- a/benchtests/README
> +++ b/benchtests/README
> @@ -27,7 +27,12 @@ BENCH_DURATION.
>  
>  The benchmark suite does function call measurements using architecture-specific
>  high precision timing instructions whenever available.  When such support is
> -not available, it uses clock_gettime (CLOCK_MONOTONIC).
> +not available, it uses clock_gettime (CLOCK_MONOTONIC).  One can force the
> +benchmark to use clock_gettime by invoking make as follows:
> +
> +  $ make USE_CLOCK_GETTIME=1 bench
> +
> +Again, one must run `make bench-clean' before changing the measurement method.
>  
>  On x86 processors, RDTSCP instruction provides more precise timing data
>  than RDTSC instruction.  All x86 processors since 2010 support RDTSCP
> diff --git a/benchtests/bench-timing.h b/benchtests/bench-timing.h
> index 5b9a8384bb..844a7727c9 100644
> --- a/benchtests/bench-timing.h
> +++ b/benchtests/bench-timing.h
> @@ -19,7 +19,11 @@
>  #undef attribute_hidden
>  #define attribute_hidden
>  #define __clock_gettime clock_gettime
> -#include <hp-timing.h>
> +#ifdef USE_CLOCK_GETTIME
> +# include <sysdeps/generic/hp-timing.h>
> +#else
> +# include <hp-timing.h>
> +#endif
>  #include <stdint.h>
>  
>  #define GL(x) _##x
> -- 
> 2.26.2
> 


-- 
Cheers,
Carlos.