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 vhlD2s0b 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000007, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Mateusz Guzik writes: > On Tue, Apr 15, 2025 at 8:14=E2=80=AFAM Ankur Arora wrote: >> >> >> Mateusz Guzik writes: >> > With that sucker out of the way, an optional quest is to figure out if >> > rep stosq vs rep stosb makes any difference for pages -- for all I kno= w >> > rep stosq is the way. This would require testing on quite a few uarchs >> > and I'm not going to blame anyone for not being interested. >> >> IIRC some recent AMD models (Rome?) did expose REP_GOOD but not ERMS. >> > > The uarch does not have it or the bit magically fails to show up? > Worst case, should rep stosb be faster on that uarch, the kernel can > pretend the bit is set. It's a synthetic bit so the uarch has both. I think REP STOSB is optimized post FSRS (AIUI Zen3) if (c->x86 >=3D 0x10) set_cpu_cap(c, X86_FEATURE_REP_GOOD); /* AMD FSRM also implies FSRS */ if (cpu_has(c, X86_FEATURE_FSRM)) set_cpu_cap(c, X86_FEATURE_FSRS); >> > Let's say nobody bothered OR rep stosb provides a win. In that case th= is >> > can trivially ALTERNATIVE between rep stosb and rep stosq based on ERM= S, >> > no func calls necessary. >> >> We shouldn't need any function calls for ERMS and REP_GOOD. >> >> I think something like this untested code should work: >> >> asm volatile( >> ALTERNATIVE_2("call clear_pages_orig", >> "rep stosb", X86_FEATURE_REP_GOOD, >> "shrl $3,%ecx; rep stosq", X86_FEATURE_ERMS, >> : "+c" (size), "+D" (addr), ASM_CALL_CONSTRAIN= T >> : "a" (0))) >> > > That's what I'm suggesting, with one difference: whack > clear_pages_orig altogether. What do we gain by getting rid of it? Maybe there's old hardware with unoptimized rep; stos*. -- ankur