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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>
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| .. | ||
| clocksource.h | ||
| getrandom.h | ||
| gettimeofday.h | ||
| processor.h | ||
| time_data.h | ||
| vsyscall.h | ||