s390/spinlock,rwlock: always to a load-and-test first

Browse source

In case a lock is contended it is better to do a load-and-test first
before trying to get the lock with compare-and-swap. This helps to avoid
unnecessary cache invalidations of the cacheline for the lock if the
CPU has to wait for the lock. For an uncontended lock doing the
compare-and-swap directly is a bit better, if the CPU does not have the
cacheline in its cache yet the compare-and-swap will get it read-write
immediately while a load-and-test would get it read-only first.

Always to the load-and-test first to avoid the cacheline invalidations
for the contended case outweight the potential read-only to read-write
cacheline upgrade for the uncontended case.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

...

This commit is contained in:

Martin Schwidefsky 2014-05-15 11:00:44 +02:00

parent 2bf29df746

commit bae8f56734

2 changed files with 46 additions and 33 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

50

arch/s390/include/asm/spinlock.h

View file

29

arch/s390/lib/spinlock.c

View file