Re: [PATCH v5 19/22] powerpc/syscall: Optimise checks in beginning of system_call_exception()

Christophe Leroy
2021-02-09T14:35:01Z

Le 09/02/2021 à 03:06, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of February 9, 2021 1:10 am:
>> Combine all tests of regs->msr into a single logical one.
>
> Okay by me unless we choose to do the config option and put these all
> under it. I think I would prefer that because sometimes the registers
> are in a state you can't easily see what the values in the expression
> were. In this case it doesn't matter so much because they should be in
> regs in the interrupt frame.

Yes indeed. I reword the commit log and tell that.

>
> Thanks,
> Nick
>
>>
>> Before the patch:
>>
>> 0: 81 6a 00 84 lwz r11,132(r10)
>> 4: 90 6a 00 88 stw r3,136(r10)
>> 8: 69 60 00 02 xori r0,r11,2
>> c: 54 00 ff fe rlwinm r0,r0,31,31,31
>> 10: 0f 00 00 00 twnei r0,0
>> 14: 69 63 40 00 xori r3,r11,16384
>> 18: 54 63 97 fe rlwinm r3,r3,18,31,31
>> 1c: 0f 03 00 00 twnei r3,0
>> 20: 69 6b 80 00 xori r11,r11,32768
>> 24: 55 6b 8f fe rlwinm r11,r11,17,31,31
>> 28: 0f 0b 00 00 twnei r11,0
>>
>> After the patch:
>>
>> 0: 81 6a 00 84 lwz r11,132(r10)
>> 4: 90 6a 00 88 stw r3,136(r10)
>> 8: 7d 6b 58 f8 not r11,r11
>> c: 71 6b c0 02 andi. r11,r11,49154
>> 10: 0f 0b 00 00 twnei r11,0
>>
>> 6 cycles less on powerpc 8xx (328 => 322 cycles).
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>> arch/powerpc/kernel/interrupt.c | 10 +++++++---
>> 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
>> index 55e1aa18cdb9..8c38e8c95be2 100644
>> --- a/arch/powerpc/kernel/interrupt.c
>> +++ b/arch/powerpc/kernel/interrupt.c
>> @@ -28,6 +28,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
>> unsigned long r0, struct pt_regs *regs)
>> {
>> syscall_fn f;
>> + unsigned long expected_msr;
>>
>> regs->orig_gpr3 = r3;
>>
>> @@ -39,10 +40,13 @@ notrace long system_call_exception(long r3, long r4, long r5,
>>
>> trace_hardirqs_off(); /* finish reconciling */
>>
>> + expected_msr = MSR_PR;
>> if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x))
>> - BUG_ON(!(regs->msr & MSR_RI));
>> - BUG_ON(!(regs->msr & MSR_PR));
>> - BUG_ON(arch_irq_disabled_regs(regs));
>> + expected_msr |= MSR_RI;
>> + if (IS_ENABLED(CONFIG_PPC32))
>> + expected_msr |= MSR_EE;
>> + BUG_ON((regs->msr & expected_msr) ^ expected_msr);
>> + BUG_ON(IS_ENABLED(CONFIG_PPC64) && arch_irq_disabled_regs(regs));
>>
>> #ifdef CONFIG_PPC_PKEY
>> if (mmu_has_feature(MMU_FTR_PKEY)) {
>> --
>> 2.25.0
>>
>>