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x86: Support RDTSCP for benchtests

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RDTSCP waits until all previous instructions have executed and all
previous loads are globally visible before reading the counter.  RDTSC
doesn't wait until all previous instructions have been executed before
reading the counter.  All x86 processors since 2010 support RDTSCP
instruction.  This patch adds RDTSCP support to benchtests.

	* benchtests/Makefile (CPPFLAGS-nonlib): Add -DUSE_RDTSCP if
	USE_RDTSCP is defined.
	* sysdeps/x86/hp-timing.h (HP_TIMING_NOW): Use RDTSCP if
	USE_RDTSCP is defined.
This commit is contained in:
H.J. Lu 2018-10-24 02:19:15 -07:00
parent 18ad0de651
commit 7cc65773f0
4 changed files with 35 additions and 1 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2018-10-24 H.J. Lu <hongjiu.lu@intel.com>
* benchtests/Makefile (CPPFLAGS-nonlib): Add -DUSE_RDTSCP if
USE_RDTSCP is defined.
* sysdeps/x86/hp-timing.h (HP_TIMING_NOW): Use RDTSCP if
USE_RDTSCP is defined.
2018-10-23 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* misc/tst-preadvwritev2-common.c (IOV_MAX): Define if not

6
benchtests/Makefile
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@ -131,6 +131,12 @@ CPPFLAGS-nonlib += -DDURATION=$(BENCH_DURATION) -D_ISOMAC
# HP_TIMING if it is available.
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 :=

9
benchtests/README
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@ -34,6 +34,15 @@ the benchmark to use clock_gettime by invoking make as follows:
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
instruction. One can force the benchmark to use RDTSCP by invoking make
as follows:
$ make USE_RDTSCP=1 bench
One must run `make bench-clean' before changing the measurement method.
Running benchmarks on another target:
====================================

12
sysdeps/x86/hp-timing.h
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@ -40,7 +40,19 @@ typedef unsigned long long int hp_timing_t;
NB: Use __builtin_ia32_rdtsc directly since including <x86intrin.h>
makes building glibc very slow. */
# ifdef USE_RDTSCP
/* RDTSCP waits until all previous instructions have executed and all
previous loads are globally visible before reading the counter.
RDTSC doesn't wait until all previous instructions have been executed
before reading the counter. */
# define HP_TIMING_NOW(Var) \
(__extension__ ({ \
unsigned int __aux; \
(Var) = __builtin_ia32_rdtscp (&__aux); \
}))
# else
# define HP_TIMING_NOW(Var) ((Var) = __builtin_ia32_rdtsc ())
# endif
# include <hp-timing-common.h>
#else