Messages in this thread | | | Date | Tue, 30 Dec 2003 02:32:09 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] optimize ia32 memmove |
| |
Linux Kernel Mailing List wrote: > ChangeSet 1.1496.22.32, 2003/12/29 21:45:30-08:00, akpm@osdl.org > > [PATCH] optimize ia32 memmove > > From: Manfred Spraul <manfred@colorfullife.com> > > The memmove implementation of i386 is not optimized: it uses movsb, which is > far slower than movsd. The optimization is trivial: if dest is less than > source, then call memcpy(). markw tried it on a 4xXeon with dbt2, it saved > around 300 million cpu ticks in cache_flusharray(): [...] > diff -Nru a/include/asm-i386/string.h b/include/asm-i386/string.h > --- a/include/asm-i386/string.h Mon Dec 29 23:13:20 2003 > +++ b/include/asm-i386/string.h Mon Dec 29 23:13:20 2003 > @@ -299,14 +299,9 @@ > static inline void * memmove(void * dest,const void * src, size_t n) > { > int d0, d1, d2; > -if (dest<src) > -__asm__ __volatile__( > - "rep\n\t" > - "movsb" > - : "=&c" (d0), "=&S" (d1), "=&D" (d2) > - :"0" (n),"1" (src),"2" (dest) > - : "memory"); > -else > +if (dest<src) { > + memcpy(dest,src,n); > +} else > __asm__ __volatile__( > "std\n\t" > "rep\n\t"
Dumb question, though... what about the overlap case, when dest<src ? It seems to me this change is ignoring that.
Jeff
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |