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powerpc: Optimise the 64bit optimised __clear_user 

I blame Mikey for this. He elevated my slightly dubious testcase:

to benchmark status. And naturally we need to be number 1 at creating
zeros. So lets improve __clear_user some more.

As Paul suggests we can use dcbz for large lengths. This patch gets
the destination cacheline aligned then uses dcbz on whole cachelines.

Before:
10485760000 bytes (10 GB) copied, 0.414744 s, 25.3 GB/s

After:
10485760000 bytes (10 GB) copied, 0.268597 s, 39.0 GB/s

39 GB/s, a new record.

Signed-off-by: Anton Blanchard <anton@samba.org>
Tested-by: Olof Johansson <olof@lixom.net>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2012-06-04 16:02:22 +00:00 committed by Benjamin Herrenschmidt
parent b4c3a8729a
commit cf8fb5533f
1 changed files with 62 additions and 1 deletions
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63
arch/powerpc/lib/string_64.S
View File

@ -19,6 +19,12 @@
*/
#include <asm/ppc_asm.h>
#include <asm/asm-offsets.h>
.section ".toc","aw"
PPC64_CACHES:
.tc ppc64_caches[TC],ppc64_caches
.section ".text"
/**
* __clear_user: - Zero a block of memory in user space, with less checking.
@ -94,9 +100,14 @@ err1; stw r0,0(r3)
addi r3,r3,4
3: sub r4,r4,r6
srdi r6,r4,5
cmpdi r4,32
cmpdi cr1,r4,512
blt .Lshort_clear
bgt cr1,.Llong_clear
.Lmedium_clear:
srdi r6,r4,5
mtctr r6
/* Do 32 byte chunks */
@ -139,3 +150,53 @@ err1; stb r0,0(r3)
10: li r3,0
blr
.Llong_clear:
ld r5,PPC64_CACHES@toc(r2)
bf cr7*4+0,11f
err2; std r0,0(r3)
addi r3,r3,8
addi r4,r4,-8
/* Destination is 16 byte aligned, need to get it cacheline aligned */
11: lwz r7,DCACHEL1LOGLINESIZE(r5)
lwz r9,DCACHEL1LINESIZE(r5)
/*
* With worst case alignment the long clear loop takes a minimum
* of 1 byte less than 2 cachelines.
*/
sldi r10,r9,2
cmpd r4,r10
blt .Lmedium_clear
neg r6,r3
addi r10,r9,-1
and. r5,r6,r10
beq 13f
srdi r6,r5,4
mtctr r6
mr r8,r3
12:
err1; std r0,0(r3)
err1; std r0,8(r3)
addi r3,r3,16
bdnz 12b
sub r4,r4,r5
13: srd r6,r4,r7
mtctr r6
mr r8,r3
14:
err1; dcbz r0,r3
add r3,r3,r9
bdnz 14b
and r4,r4,r10
cmpdi r4,32
blt .Lshort_clear
b .Lmedium_clear