Commit 823df435 authored Apr 04, 2012 by Anton Blanchard Committed by Benjamin Herrenschmidt Apr 30, 2012

powerpc: No need to save XER in a system call



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>

parent d14299de

arch/powerpc/kernel/entry_64.S

+1 −2

Original line number	Diff line number	Diff line
		@@ -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)