From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: [RFC PATCH] powerpc/6xx: Don't set back MSR_RI before reenabling MMU
Date: Thu, 31 Jan 2019 17:44:54 +0000 (UTC) [thread overview]
Message-ID: <9f9dd859d571e324c7412ed9db9da8cfba678257.1548956511.git.christophe.leroy@c-s.fr> (raw)
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
next reply other threads:[~2019-01-31 17:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-31 17:44 Christophe Leroy [this message]
2019-02-01 11:10 ` [RFC PATCH] powerpc/6xx: Don't set back MSR_RI before reenabling MMU Michael Ellerman
2019-02-01 11:51 ` Christophe Leroy
2019-02-12 13:24 ` Christophe Leroy
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