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.
Use __builtin_ia32_rdtsc directly since including <x86intrin.h> makes
building glibc very slow. On Intel Core i5-6260U, this patch reduces
x86-64 build time from 8 minutes 33 seconds to 3 minutes 48 seconds
with "make -j4" and GCC 8.2.1.
* sysdeps/x86/hp-timing.h: Don't include <x86intrin.h>.
(HP_TIMING_NOW): Replace _rdtsc with __builtin_ia32_rdtsc.
Since _rdtsc intrinsic is supported in GCC 4.9, we can use it for
HP_TIMING_NOW. This patch
1. Create x86 hp-timing.h to replace i686 and x86_64 hp-timing.h.
2. Move MINIMUM_ISA from init-arch.h to isa.h so that x86 hp-timing.h
can check minimum x86 ISA to decide if _rdtsc can be used.
NB: Checking if __i686__ isn't sufficient since __i686__ may not be
defined when building for i686 class processors.
* sysdeps/i386/init-arch.h: Removed.
* sysdeps/i386/i586/init-arch.h: Likewise.
* sysdeps/i386/i686/init-arch.h: Likewise.
* sysdeps/i386/i686/hp-timing.h: Likewise.
* sysdeps/x86_64/hp-timing.h: Likewise.
* sysdeps/i386/isa.h: New file.
* sysdeps/i386/i586/isa.h: Likewise.
* sysdeps/i386/i686/isa.h: Likewise.
* sysdeps/x86_64/isa.h: Likewise.
* sysdeps/x86/hp-timing.h: New file.
* sysdeps/x86/init-arch.h: Include <isa.h>.
