s390/bitops: optimize set_bit() for constant values

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Since zEC12 we have the interlocked-access facility 2 which allows to
use the instructions ni/oi/xi to update a single byte in storage with
compare-and-swap semantics.
So change set_bit(), clear_bit() and change_bit() to generate such code
instead of a compare-and-swap loop (or using the load-and-* instruction
family), if possible.
This reduces the text segment by yet another 8KB (defconfig).

Alternatively the long displacement variants niy/oiy/xiy could have
been used, but the extended displacement field is usually not needed
and therefore would only increase the size of the text segment again.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

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Heiko Carstens 2013-09-17 09:48:44 +02:00 • committed by Martin Schwidefsky

parent 370b0b5f77

commit 4ae803253e

2 changed files with 37 additions and 1 deletions

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36

arch/s390/include/asm/bitops.h

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2

arch/s390/kernel/head.S

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