path: root/arch/s390/include/asm/string.h
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authorHeiko Carstens <hca@linux.ibm.com>2020-12-04 12:32:42 +0100
committerHeiko Carstens <hca@linux.ibm.com>2020-12-16 14:55:49 +0100
commitdd6cfe553212b6311cac27ecd2f67621857fb10a (patch)
tree75a5501adcd811dd9647cd7835d98fafdee32b8c /arch/s390/include/asm/string.h
parent91c2bad6aec98a51663ce9eec7c4825c1ca0b870 (diff)
s390/delay: simplify udelay
udelay is implemented by using quite subtle details to make it possible to load an idle psw and waiting for an interrupt even in irq context or when interrupts are disabled. Also handling (or better: no handling) of softirqs is taken into account. All this is done to optimize for something which should in normal circumstances never happen: calling udelay to busy wait. Therefore get rid of the whole complexity and just busy loop like other architectures are doing it also. It could have been possible to use diag 0x44 instead of cpu_relax() in the busy loop, however we have seen too many bad things happen with diag 0x44 that it seems to be better to simply busy loop. Also note that with this new implementation kernel preemption does work when within the udelay loop. This did not work before. To get a feeling what the former code optimizes for: IPL'ing a kernel with 'defconfig' and afterwards compiling a kernel ends with a total of zero udelay calls. Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'arch/s390/include/asm/string.h')
0 files changed, 0 insertions, 0 deletions

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