Messages in this thread | | | Date | Fri, 13 Nov 2009 00:04:54 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by fast string. |
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On 11/12/2009 11:33 PM, Ingo Molnar wrote: > > * Pavel Machek <pavel@ucw.cz> wrote: > >>> Ling, if you are interested, could you send a user-space test-app to >>> this thread that everyone could just compile and run on various older >>> boxes, to gather a performance profile of hand-coded versus string ops >>> performance? >>> >>> ( And i think we can make a judgement based on cache-hot performance >>> alone - if then the strings ops will perform comparatively better in >>> cache-cold scenarios, so the cache-hot numbers would be a conservative >>> estimate. ) >> >> Ugh, really? I'd expect cache-cold performance to be not helped at all >> (memory bandwidth limit) and you'll get slow down from additional >> i-cache misses... > > That's my point - the new code is shorter, which will run comparatively > faster in a cache-cold environment. >
memcpy_c by itself is by far the shortest variant, of course.
The question is if it makes sense to use the long variants for short (< 1024 bytes) copies.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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