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powerpc/64s: Optimise MSR handling in exception handling

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mtmsrd with L=1 only affects MSR_EE and MSR_RI bits, and we always
know what state those bits are, so the kernel MSR does not need to be
loaded when modifying them.

mtmsrd is often in the critical execution path, so avoiding dependency
on even L1 load is noticable. On a POWER8 this saves about 3 cycles
from the syscall path, and possibly a few from other exception returns
(not measured).

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2016-09-15 19:04:46 +10:00 committed by Michael Ellerman
parent 18e3f56b1c
commit 49d09bf2a6
1 changed files with 9 additions and 12 deletions
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21
arch/powerpc/kernel/entry_64.S
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@ -139,7 +139,7 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR)
#ifdef CONFIG_PPC_BOOK3E
wrteei 1
#else
ld r11,PACAKMSR(r13)
li r11,MSR_RI
ori r11,r11,MSR_EE
mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
@ -195,7 +195,6 @@ system_call: /* label this so stack traces look sane */
#ifdef CONFIG_PPC_BOOK3E
wrteei 0
#else
ld r10,PACAKMSR(r13)
/*
* For performance reasons we clear RI the same time that we
* clear EE. We only need to clear RI just before we restore r13
@ -203,8 +202,7 @@ system_call: /* label this so stack traces look sane */
* We have to be careful to restore RI if we branch anywhere from
* here (eg syscall_exit_work).
*/
li r9,MSR_RI
andc r11,r10,r9
li r11,0
mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
@ -221,13 +219,12 @@ system_call: /* label this so stack traces look sane */
#endif
2: addi r3,r1,STACK_FRAME_OVERHEAD
#ifdef CONFIG_PPC_BOOK3S
li r10,MSR_RI
mtmsrd r10,1 /* Restore RI */
#endif
bl restore_math
#ifdef CONFIG_PPC_BOOK3S
ld r10,PACAKMSR(r13)
li r9,MSR_RI
andc r11,r10,r9 /* Re-clear RI */
li r11,0
mtmsrd r11,1
#endif
ld r8,_MSR(r1)
@ -308,6 +305,7 @@ syscall_enosys:
syscall_exit_work:
#ifdef CONFIG_PPC_BOOK3S
li r10,MSR_RI
mtmsrd r10,1 /* Restore RI */
#endif
/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
@ -354,7 +352,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
#ifdef CONFIG_PPC_BOOK3E
wrteei 1
#else
ld r10,PACAKMSR(r13)
li r10,MSR_RI
ori r10,r10,MSR_EE
mtmsrd r10,1
#endif /* CONFIG_PPC_BOOK3E */
@ -619,7 +617,7 @@ _GLOBAL(ret_from_except_lite)
#ifdef CONFIG_PPC_BOOK3E
wrteei 0
#else
ld r10,PACAKMSR(r13) /* Get kernel MSR without EE */
li r10,MSR_RI
mtmsrd r10,1 /* Update machine state */
#endif /* CONFIG_PPC_BOOK3E */
@ -751,7 +749,7 @@ resume_kernel:
#ifdef CONFIG_PPC_BOOK3E
wrteei 0
#else
ld r10,PACAKMSR(r13) /* Get kernel MSR without EE */
li r10,MSR_RI
mtmsrd r10,1 /* Update machine state */
#endif /* CONFIG_PPC_BOOK3E */
#endif /* CONFIG_PREEMPT */
@ -841,8 +839,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
* userspace and we take an exception after restoring r13,
* we end up corrupting the userspace r13 value.
*/
ld r4,PACAKMSR(r13) /* Get kernel MSR without EE */
andc r4,r4,r0 /* r0 contains MSR_RI here */
li r4,0
mtmsrd r4,1
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM