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SubjectRe: [PATCH v5 3/3] powerpc/lib: optimise PPC32 memcmp
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Le 29/05/2018 à 22:03, Mathieu Malaterre a écrit :
> On Mon, May 28, 2018 at 12:49 PM, Christophe Leroy
> <christophe.leroy@c-s.fr> wrote:
>> At the time being, memcmp() compares two chunks of memory
>> byte per byte.
>>
>> This patch optimises the comparison by comparing word by word.
>>
>> A small benchmark performed on an 8xx comparing two chuncks
>> of 512 bytes performed 100000 times gives:
>>
>> Before : 5852274 TB ticks
>> After: 1488638 TB ticks
>>
>> This is almost 4 times faster
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>> ---
>> arch/powerpc/lib/string_32.S | 37 +++++++++++++++++++++++++++----------
>> 1 file changed, 27 insertions(+), 10 deletions(-)
>
> Would it possible for you to move the actual code instead to:
>
> ./arch/powerpc/lib/memcmp_32.S
>
> This will seat right next to memcmp_64.S implementation.

Good idea, thanks.
Done in v6

Christophe

>
>> diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
>> index 40a576d56ac7..4fbaa046aa84 100644
>> --- a/arch/powerpc/lib/string_32.S
>> +++ b/arch/powerpc/lib/string_32.S
>> @@ -16,17 +16,34 @@
>> .text
>>
>> _GLOBAL(memcmp)
>> - cmpwi cr0, r5, 0
>> - beq- 2f
>> - mtctr r5
>> - addi r6,r3,-1
>> - addi r4,r4,-1
>> -1: lbzu r3,1(r6)
>> - lbzu r0,1(r4)
>> - subf. r3,r0,r3
>> - bdnzt 2,1b
>> + srawi. r7, r5, 2 /* Divide len by 4 */
>> + mr r6, r3
>> + beq- 3f
>> + mtctr r7
>> + li r7, 0
>> +1: lwzx r3, r6, r7
>> + lwzx r0, r4, r7
>> + addi r7, r7, 4
>> + cmplw cr0, r3, r0
>> + bdnzt eq, 1b
>> + bne 5f
>> +3: andi. r3, r5, 3
>> + beqlr
>> + cmplwi cr1, r3, 2
>> + blt- cr1, 4f
>> + lhzx r3, r6, r7
>> + lhzx r0, r4, r7
>> + addi r7, r7, 2
>> + subf. r3, r0, r3
>> + beqlr cr1
>> + bnelr
>> +4: lbzx r3, r6, r7
>> + lbzx r0, r4, r7
>> + subf. r3, r0, r3
>> blr
>> -2: li r3,0
>> +5: li r3, 1
>> + bgtlr
>> + li r3, -1
>> blr
>> EXPORT_SYMBOL(memcmp)
>>
>> --
>> 2.13.3
>>

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