s390/percpu: Provide arch_raw_cpu_ptr()

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Provide an s390 specific arch_raw_cpu_ptr() implementation which avoids the
detour over get_lowcore() to get the lowcore pointer. The inline assembly
is implemented with an alternative so that relocated lowcore (percpu offset
is at a different address) is handled correctly.

This turns code like this

  102f78:       a7 39 00 00             lghi    %r3,0
  102f7c:       e3 20 33 b8 00 08       ag      %r2,952(%r3)

which adds the percpu offset to register r2 into a single instruction

  102f7c:       e3 20 33 b8 00 08       ag      %r2,952(%r0)

and also avoids the need of a base register, thus reducing register
pressure.

With defconfig bloat-o-meter -t provides this result:

add/remove: 12/26 grow/shrink: 183/3391 up/down: 14880/-41950 (-27070)

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

...

This commit is contained in:

Heiko Carstens 2026-03-17 20:54:28 +01:00 • committed by Vasily Gorbik

parent 7bbf70131f

commit fa8be59ce2

1 changed files with 18 additions and 0 deletions

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arch/s390/include/asm/percpu.h

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