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powerpc: No need to save XER in a system call

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The XER is a volatile register so there is no need to save and restore
it over a system call - zero it out in the exception stack frame
instead.

This should fix a 5 cycle stall of the mfxer/std seen on POWER7.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2012-04-04 18:24:29 +00:00 committed by Benjamin Herrenschmidt
parent d14299dec7
commit 823df43552
1 changed files with 1 additions and 2 deletions
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arch/powerpc/kernel/entry_64.S
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@ -82,6 +82,7 @@ system_call_common:
std r11,GPR10(r1)
std r11,GPR11(r1)
std r11,GPR12(r1)
std r11,_XER(r1)
std r9,GPR13(r1)
mfcr r9
mflr r10
@ -89,9 +90,7 @@ system_call_common:
std r9,_CCR(r1)
std r10,_LINK(r1)
std r11,_TRAP(r1)
mfxer r9
mfctr r10
std r9,_XER(r1)
std r10,_CTR(r1)
std r3,ORIG_GPR3(r1)
ld r2,PACATOC(r13)