Messages in this thread | | | Date | Mon, 15 Aug 2011 22:05:10 +0200 | From | Borislav Petkov <> | Subject | Re: x86 memcpy performance |
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On Mon, Aug 15, 2011 at 03:11:40PM -0400, Andrew Lutomirski wrote: > > Well, copy_from_user... does a bunch of rep; movsq - if the SSE version > > shows reasonable speedup there, we might need to make those work too. > > I'm a little surprised that SSE beats fast string operations, but I > guess benchmarking always wins.
If by fast string operations you mean X86_FEATURE_ERMS, then that's Intel-only and that actually would need to be benchmarked separately. Currently, I see speedup for large(r) buffers only vs rep; movsq. But I dunno about rep; movsb's enhanced rep string tricks Intel does.
> Yes. But we don't nest that much, and the save/restore isn't all that > expensive. And we don't have to save/restore unless kernel entries > nest and both entries try to use kernel_fpu_begin at the same time.
Yep.
> This whole project may take awhile. The code in there is a > poorly-documented mess, even after Hans' cleanups. (It's a lot worse > without them, though.)
Oh yeah, this code could use lotsa scrubbing :)
-- Regards/Gruss, Boris.
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