mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-08-09 06:14:34 +02:00
Heiko CarstensandAlexander Gordeev
44e5edace5
There are many loops in the form of
while (READ_ONCE(*somelocation))
cpu_relax();
Strictly speaking the architecture requires serialization instead of only a
compiler barrier in the loop so the READ_ONCE() will see an updated value.
However real hardware does not require this (see IBM z Systems Processor
Optimization Primer - FAQ [1]), but it is still recommended to add
serialization. Given that cpu_relax() is doing nothing useful, it does
not hurt to add the single and fast instruction which makes sure that
serialization happens, and such loops may be left a bit faster.
[1] https://community.ibm.com/community/user/viewdocument/microprocessor-optimization-primer
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
10 lines
206 B
C
10 lines
206 B
C
/* SPDX-License-Identifier: GPL-2.0-only */
|
|
#ifndef __ASM_VDSO_PROCESSOR_H
|
|
#define __ASM_VDSO_PROCESSOR_H
|
|
|
|
#include <asm/barrier.h>
|
|
|
|
#define cpu_relax() bcr_serialize()
|
|
|
|
#endif /* __ASM_VDSO_PROCESSOR_H */
|