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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Massive slowdown under specific memcpy implementations (32bit, no-SIMD, backward copy)."
href="https://bugs.freedesktop.org/show_bug.cgi?id=107670#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Massive slowdown under specific memcpy implementations (32bit, no-SIMD, backward copy)."
href="https://bugs.freedesktop.org/show_bug.cgi?id=107670">bug 107670</a>
from <span class="vcard"><a class="email" href="mailto:iive@yahoo.com" title="iive@yahoo.com">iive@yahoo.com</a>
</span></b>
<pre>(In reply to Timothy Arceri from <a href="show_bug.cgi?id=107670#c1">comment #1</a>)
<span class="quote">> 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.</span >
Because some implementations copy data backwards and this creates a huge
problem when it is written over PCIe.
To be clear:
for(i=0;i<size;i++) dst[i]=src[i]; // forward copy.
for(i=size-1;i>=0;i--) dst[i]=src[i]; // backwards copy</pre>
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