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 <an...@samba.org>
---
Index: linux-build/arch/powerpc/kernel/entry_64.S
===================================================================
--- linux-build.orig/arch/powerpc/kernel/entry_64.S 2012-03-22
22:47:04.479314599 +1100
+++ linux-build/arch/powerpc/kernel/entry_64.S 2012-03-22 22:47:08.379384827
+1100
@@ -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)
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