Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 5 Jun 2018 16:27:24 -0700 | Subject | Re: x86/asm: __clear_user() micro-optimization (was: "Re: [GIT PULL] x86/asm changes for v4.18") |
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On Tue, Jun 5, 2018 at 4:20 PM Alexey Dobriyan <adobriyan@gmail.com> wrote: > > This is Broadwell Xeon E5-2620 v4. > Which is somewhat strange indeed because it should be modern enough.
Yeah, odd.
Here's the benchmark I used:
#define SIZE 4068
int main(int argc, char **argv) { int i; unsigned char buffer[SIZE], *p;
for (i = 0; i < 1000000; i++) asm volatile( "1: movq %[zero],(%[mem]); addq %[eight],%[mem]; decl %[count]; jne 1b" : [mem] "=r" (p) : [zero] "i" (0l), [eight] "i" (8l), "0" (buffer), [count] "r" (SIZE/8)); }
where you can change that "i" for [zero] and [eight] to be "r" to get the register version.
I just timed it, because I'm lazy and perf seemed to be overkill.
It might be some very specific loop buffer issue or something.
Or maybe my benchmark above is broken, I didn't really verify that the end result was any good (I just did an objdump to verify the asm code superficially).
Linus
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