github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-07-27 09:36:22 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph

s390/processor: Implement cpu_relax() with cpu serialization

Browse Source 
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>
This commit is contained in:
Heiko Carstens 2026-05-08 17:02:48 +02:00 committed by Alexander Gordeev
parent 24b3afcff4
commit 44e5edace5
1 changed files with 3 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/s390/include/asm/vdso/processor.h
View File

@ -2,6 +2,8 @@
#ifndef __ASM_VDSO_PROCESSOR_H
#define __ASM_VDSO_PROCESSOR_H
#define cpu_relax() barrier()
#include <asm/barrier.h>
#define cpu_relax() bcr_serialize()
#endif /* __ASM_VDSO_PROCESSOR_H */