Messages in this thread | | | Date | Wed, 6 Jun 2018 02:20:22 +0300 | From | Alexey Dobriyan <> | 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 05, 2018 at 04:04:37PM -0700, Linus Torvalds wrote: > On Tue, Jun 5, 2018 at 4:01 PM Linus Torvalds > <torvalds@linux-foundation.org> wrote: > > > > On Tue, Jun 5, 2018 at 3:41 PM Alexey Dobriyan <adobriyan@gmail.com> wrote: > > > > > > On my potato performance increase is 33%, sheesh. > > > And CPU starts doing 3 instructions per cycle vs 2. > > > > Whee. That's a shockingly big difference. On my CPU (i7-6700K) it > > makes absolutely no difference whether the values are integers or in > > registers. > > In fact, looking at Agner Fog's instruction lists, I don't see any CPU > where it would make a difference, except for the P4 (where the > immediate looks like it's a bad idea because it's an extra uop, but it > might pack fine and not be noticeable). > > But maybe I'm missing something subtle. What CPU, out of morbid interest?
This is Broadwell Xeon E5-2620 v4. Which is somewhat strange indeed because it should be modern enough.
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