Re: SLRU optimization - configurable buffer pool and partitioning the SLRU lock

Andrey M. Borodin <x4mmm(at)yandex-team(dot)ru> 于2023年12月14日周四 17:35写道：

>
>
> > On 14 Dec 2023, at 14:28, tender wang <tndrwang(at)gmail(dot)com> wrote:
> >
> > Now that AND is more faster, Can we replace the '%
> SLRU_MAX_BANKLOCKS' operation in SimpleLruGetBankLock() with '& 127'
>
> unsigned int GetBankno1(unsigned int pageno) {
> return pageno & 127;
> }
>
> unsigned int GetBankno2(unsigned int pageno) {
> return pageno % 128;
> }
>
> Generates with -O2
>
> GetBankno1(unsigned int):
> mov eax, edi
> and eax, 127
> ret
> GetBankno2(unsigned int):
> mov eax, edi
> and eax, 127
> ret
>
>
> Compiler is smart enough with constants.
>

Yeah, that's true.

int GetBankno(long pageno) {
unsigned short bank_mask = 128;
int bankno = (pageno & bank_mask) % 128;
return bankno;
}
enable -O2, only one instruction:
xor eax, eax

But if we all use '%', thing changs as below:
int GetBankno(long pageno) {
unsigned short bank_mask = 128;
int bankno = (pageno % bank_mask) % 128;
return bankno;
}
mov rdx, rdi
sar rdx, 63
shr rdx, 57
lea rax, [rdi+rdx]
and eax, 127
sub eax, edx

> Best regards, Andrey Borodin.