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Subject[RFC PATCH] powerpc/6xx: Don't set back MSR_RI before reenabling MMU
Date
By delaying the setting of MSR_RI, a 1% improvment is optained on
null_syscall selftest on an mpc8321.

Without this patch:

root@vgoippro:~# ./null_syscall
1134.33 ns 378.11 cycles

With this patch:

root@vgoippro:~# ./null_syscall
1121.85 ns 373.95 cycles

The drawback is that a machine check during that period
would be unrecoverable, but as only main memory is accessed
during that period, it shouldn't be a concern.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/kernel/head_32.S | 2 --
1 file changed, 2 deletions(-)

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 146385b1c2da..ea28a6ab56ec 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -282,8 +282,6 @@ __secondary_hold_acknowledge:
stw r1,GPR1(r11); \
stw r1,0(r11); \
tovirt(r1,r11); /* set new kernel sp */ \
- li r10,MSR_KERNEL & ~(MSR_IR|MSR_DR); /* can take exceptions */ \
- MTMSRD(r10); /* (except for mach check in rtas) */ \
stw r0,GPR0(r11); \
lis r10,STACK_FRAME_REGS_MARKER@ha; /* exception frame marker */ \
addi r10,r10,STACK_FRAME_REGS_MARKER@l; \
--
2.13.3
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