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powerpc: Better scheduling of CR save code in system call path

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At the moment system call entry looks like:

crclr	so
...
mfcr	r9
...
std	r9,_CCR(r1)

commit bd19c8994a ([POWERPC] system call micro optimisation) put
some space between the crclr and mfcr in order to avoid a stall.

There is still a stall seen between the mfcr and std. We can avoid
the crclr by doing it in a GPR with rlwinm which gives us more room
to better schedule the sequence.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2012-04-05 03:44:48 +00:00 committed by Benjamin Herrenschmidt
parent 82087414c6
commit fd6c40f3b0
1 changed files with 7 additions and 9 deletions
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16
arch/powerpc/kernel/entry_64.S
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@ -63,15 +63,9 @@ system_call_common:
std r0,GPR0(r1)
std r10,GPR1(r1)
ACCOUNT_CPU_USER_ENTRY(r10, r11)
/*
* This "crclr so" clears CR0.SO, which is the error indication on
* return from this system call. There must be no cmp instruction
* between it and the "mfcr r9" below, otherwise if XER.SO is set,
* CR0.SO will get set, causing all system calls to appear to fail.
*/
crclr so
std r2,GPR2(r1)
std r3,GPR3(r1)
mfcr r2
std r4,GPR4(r1)
std r5,GPR5(r1)
std r6,GPR6(r1)
@ -85,13 +79,17 @@ system_call_common:
std r11,_XER(r1)
std r11,_CTR(r1)
std r9,GPR13(r1)
mfcr r9
mflr r10
/*
* This clears CR0.SO (bit 28), which is the error indication on
* return from this system call.
*/
rldimi r2,r11,28,(63-28)
li r11,0xc01
std r9,_CCR(r1)
std r10,_LINK(r1)
std r11,_TRAP(r1)
std r3,ORIG_GPR3(r1)
std r2,_CCR(r1)
ld r2,PACATOC(r13)
addi r9,r1,STACK_FRAME_OVERHEAD
ld r11,exception_marker@toc(r2)