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Age	Commit message (Collapse)	Author
2026-05-20	s390/processor: Implement cpu_relax() with cpu serialization	Heiko Carstens
	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>
2020-08-26	s390: convert to GENERIC_VDSO	Sven Schnelle
	Convert s390 to generic vDSO. There are a few special things on s390: - vDSO can be called without a stack frame - glibc did this in the past. So we need to allocate a stackframe on our own. - The former assembly code used stcke to get the TOD clock and applied time steering to it. We need to do the same in the new code. This is done in the architecture specific __arch_get_hw_counter function. The steering information is stored in an architecure specific area in the vDSO data. - CPUCLOCK_VIRT is now handled with a syscall fallback, which might be slower/less accurate than the old implementation. The getcpu() function stays as an assembly function because there is no generic implementation and the code is just a few lines. Performance number from my system do 100 mio gettimeofday() calls: Plain syscall: 8.6s Generic VDSO: 1.3s old ASM VDSO: 1s So it's a bit slower but still much faster than syscalls. Signed-off-by: Sven Schnelle <svens@linux.ibm.com> Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>