s390/preempt: Optimize __preemp_count_add()/__preempt_count_sub()

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Provide an inline assembly using alternatives to avoid the need of a
base register due to relocatable lowcore when adding or subtracting
small constants from preempt_count.

Main user is preempt_disable(), which subtracts one from
preempt_count. With this the generated code changes from

  10012c:       a7 b9 00 00             lghi    %r11,0
  100130:       eb 01 b3 a8 00 6a       asi     936(%r11),1

to something like this:

 10012c:        eb 01 03 a8 00 6a       asi     936,1

Kernel image size is reduced by 13kb (bloat-o-meter -t, defconfig, gcc15).

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

...

This commit is contained in:

Heiko Carstens 2026-01-13 20:43:58 +01:00

parent 6cce3609a1

commit 23ba7d3163

1 changed files with 11 additions and 1 deletions

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arch/s390/include/asm/preempt.h

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