Commit 993fef95 authored Oct 04, 2017 by Heiko Carstens Committed by Martin Schwidefsky Oct 09, 2017

s390: optimize memset implementation



Like for the memset16/32/64 variants avoid that subsequent mvc
instructions depend on each other since that might have negative
performance impacts.

This patch is currently hardly relevant since at least gcc 7.1
generates only inline memset code and not a single memset call.
However there is no reason to not provide an optimized version
just in case gcc generates memset calls again, like it did in
the past.

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

parent 41879ff6

arch/s390/lib/mem.S

+12 −8

Original line number	Diff line number	Diff line
		@@ -78,21 +78,25 @@ ENTRY(memset)
		ex %r4,0(%r3)
		br %r14
		.Lmemset_fill:
		stc %r3,0(%r2)
		cghi %r4,1
		lgr %r1,%r2
		ber %r14
		je .Lmemset_fill_exit
		aghi %r4,-2
		srlg %r3,%r4,8
		ltgr %r3,%r3
		srlg %r5,%r4,8
		ltgr %r5,%r5
		jz .Lmemset_fill_remainder
		.Lmemset_fill_loop:
		mvc 1(256,%r1),0(%r1)
		stc %r3,0(%r1)
		mvc 1(255,%r1),0(%r1)
		la %r1,256(%r1)
		brctg %r3,.Lmemset_fill_loop
		brctg %r5,.Lmemset_fill_loop
		.Lmemset_fill_remainder:
		larl %r3,.Lmemset_mvc
		ex %r4,0(%r3)
		stc %r3,0(%r1)
		larl %r5,.Lmemset_mvc
		ex %r4,0(%r5)
		br %r14
		.Lmemset_fill_exit:
		stc %r3,0(%r1)
		br %r14
		.Lmemset_xc:
		xc 0(1,%r1),0(%r1)

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