On Fri, Jun 25, 2010 at 08:27:20PM +0200, Vladimir 'φ-coder/phcoder' Serbinenko
wrote:
> > +void *
> > +grub_memset (void *s, int c, grub_size_t n)
> > +{
> > + unsigned char *p = (unsigned char *) s;
> > +
> > + while (n--)
> > + *p++ = (unsigned char) c;
> > +
> > + return s;
> > +}
>
> Attached is a possible generic implementation. Not even compile-tested.
> Could you test it and compare disasm of this version on i386 and glibc
> i386 version. Perhaps they are equivalent. If they are for maintainance
> reasons it's better to always use generic one.
Thanks for this, and sorry for my delay.
I haven't compared the disassembly, but once I fixed up your code it
performed within about 10% of the optimised version I posted before, so
about 640ms original, 160ms with i386-specific memset, and 176ms with
your generic memset. Even though that isn't quite equivalent, I don't
think that 16ms is going to be a major problem, and so I would suggest
going with the generic version. Please check the following.
2010-07-23 Vladimir Serbinenko <phco...@gmail.com>
2010-07-23 Colin Watson <cjwat...@ubuntu.com>
* kern/misc.c (grub_memset): Optimise to reduce cache stalls.
=== modified file 'kern/misc.c'
--- kern/misc.c 2010-07-02 17:35:07 +0000
+++ kern/misc.c 2010-07-23 11:05:32 +0000
@@ -518,12 +518,39 @@ grub_strndup (const char *s, grub_size_t
}
void *
-grub_memset (void *s, int c, grub_size_t n)
+grub_memset (void *s, int c, grub_size_t len)
{
- unsigned char *p = (unsigned char *) s;
+ void *p = s;
+ grub_uint8_t pattern8 = c;
- while (n--)
- *p++ = (unsigned char) c;
+ if (len >= 3 * sizeof (unsigned long))
+ {
+ unsigned long patternl = 0;
+ grub_size_t i;
+
+ for (i = 0; i < sizeof (unsigned long); i++)
+ patternl |= ((unsigned long) pattern8) << (8 * i);
+
+ while (len > 0 && (((grub_addr_t) p) & (sizeof (unsigned long) - 1)))
+ {
+ *(grub_uint8_t *) p = pattern8;
+ p = (grub_uint8_t *) p + 1;
+ len--;
+ }
+ while (len >= sizeof (unsigned long))
+ {
+ *(unsigned long *) p = patternl;
+ p = (unsigned long *) p + 1;
+ len -= sizeof (unsigned long);
+ }
+ }
+
+ while (len > 0)
+ {
+ *(grub_uint8_t *) p = pattern8;
+ p = (grub_uint8_t *) p + 1;
+ len--;
+ }
return s;
}
--
Colin Watson [cjwat...@ubuntu.com]
_______________________________________________
Grub-devel mailing list
Grub-devel@gnu.org
http://lists.gnu.org/mailman/listinfo/grub-devel
