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| author | Nicholas Piggin <npiggin@gmail.com> | 2017-06-08 17:35:05 +0200 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-06-15 08:34:39 +0200 |
| commit | bc4f65e4cf9d6cc43e0e9ba0b8648cf9201cd55f (patch) | |
| tree | dcc4f6b0f90b5533b887651f93f38dd780f0d23a /arch/powerpc/kernel/entry_64.S | |
| parent | powerpc/64s: Optimize hypercall/syscall entry (diff) | |
| download | linux-bc4f65e4cf9d6cc43e0e9ba0b8648cf9201cd55f.tar.xz linux-bc4f65e4cf9d6cc43e0e9ba0b8648cf9201cd55f.zip | |
powerpc/64: Avoid restore_math call if possible in syscall exit
The syscall exit code that branches to restore_math is quite heavy on
Book3S, consisting of 2 mtmsr instructions. Threads that don't use both
FP and vector can get caught here if the kernel ever uses FP or vector.
Lazy-FP/vec context switching also trips this case.
So check for lazy FP and vector before switching RI for restore_math.
Move most of this case out of line.
For threads that do want to restore math registers, the MSR switches are
still suboptimal. Future direction may be to use a soft-RI bit to avoid
MSR switches in kernel (similar to soft-EE), but for now at least the
no-restore
POWER9 context switch rate increases by about 5% due to sched_yield(2)
return performance. I haven't constructed a test to measure the syscall
cost.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/entry_64.S')
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 62 |
1 files changed, 43 insertions, 19 deletions
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index bfbad08a1207..6f70ea821a07 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -210,27 +210,17 @@ system_call: /* label this so stack traces look sane */ andi. r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK) bne- syscall_exit_work - andi. r0,r8,MSR_FP - beq 2f + /* If MSR_FP and MSR_VEC are set in user msr, then no need to restore */ + li r7,MSR_FP #ifdef CONFIG_ALTIVEC - andis. r0,r8,MSR_VEC@h - bne 3f + oris r7,r7,MSR_VEC@h #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 - li r11,0 - mtmsrd r11,1 -#endif - ld r8,_MSR(r1) - ld r3,RESULT(r1) - li r11,-MAX_ERRNO + and r0,r8,r7 + cmpd r0,r7 + bne syscall_restore_math +.Lsyscall_restore_math_cont: -3: cmpld r3,r11 + cmpld r3,r11 ld r5,_CCR(r1) bge- syscall_error .Lsyscall_error_cont: @@ -263,7 +253,41 @@ syscall_error: neg r3,r3 std r5,_CCR(r1) b .Lsyscall_error_cont - + +syscall_restore_math: + /* + * Some initial tests from restore_math to avoid the heavyweight + * C code entry and MSR manipulations. + */ + LOAD_REG_IMMEDIATE(r0, MSR_TS_MASK) + and. r0,r0,r8 + bne 1f + + ld r7,PACACURRENT(r13) + lbz r0,THREAD+THREAD_LOAD_FP(r7) +#ifdef CONFIG_ALTIVEC + lbz r6,THREAD+THREAD_LOAD_VEC(r7) + add r0,r0,r6 +#endif + cmpdi r0,0 + beq .Lsyscall_restore_math_cont + +1: 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 + li r11,0 + mtmsrd r11,1 +#endif + /* Restore volatiles, reload MSR from updated one */ + ld r8,_MSR(r1) + ld r3,RESULT(r1) + li r11,-MAX_ERRNO + b .Lsyscall_restore_math_cont + /* Traced system call support */ syscall_dotrace: bl save_nvgprs |