[Mesa-dev] [Bug 107670] Massive slowdown under specific memcpy implementations (32bit, no-SIMD, backward copy).

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Thu Aug 30 23:45:13 UTC 2018


Timothy Arceri <t_arceri at yahoo.com.au> changed:

           What    |Removed                     |Added
             Status|NEW                         |NEEDINFO

--- Comment #8 from Timothy Arceri <t_arceri at yahoo.com.au> ---
(In reply to Eero Tamminen from comment #6)
> (In reply to Timothy Arceri from comment #1)
> > There already is asm optimized version of memcpy() in glibc. Why would we
> > want to reinvent that in Mesa?
> > 
> > glibc should pick the right implementation for you system.
> How would memcpy() know that the destination is mapped to PCI-E address
> space i.e. gets transparently transferred over the PCI-E bus (which has its
> own performance constraints)?

"The slowdown could be observed if non-SIMD version of the glibc-2.27 function
is used (like the one that comes with the 32 bit Slackware-current). 


Using SSE2 memcpy seems to avoid this problem"

Glib should select the SSE2 (or better) version of memcpy. If Slackware doesn't
ship and SSE2 support for glibc I don't see how this is Mesas fault.

If I'm misunderstanding somthing please clarify. Otherwise I'm inclined to
close this as won't fix.

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