In arch/i386/lib/mmx.c there is a function fast_copy_page() using some
crafty asm statements. However I don't quite understand the part with the
fixup sections?! Can anybody shed some light into was is going on here?!
----- arch/i386/lib/mmx.c
static void fast_copy_page(void *to, void *from)
{
int i;
kernel_fpu_begin();
/* maybe the prefetch stuff can go before the expensive fnsave...
* but that is for later. -AV
*/
__asm__ __volatile__ (
"1: prefetch (%0)\n"
" prefetch 64(%0)\n"
" prefetch 128(%0)\n"
" prefetch 192(%0)\n"
" prefetch 256(%0)\n"
"2: \n"
".section .fixup, \"ax\"\n"
"3: movw $0x1AEB, 1b\n" /* jmp on 26 bytes */
" jmp 2b\n"
".previous\n"
".section __ex_table,\"a\"\n"
" .align 4\n"
" .long 1b, 3b\n"
".previous"
: : "r" (from) );
for(i=0; i<(4096-320)/64; i++)
{
__asm__ __volatile__ (
"1: prefetch 320(%0)\n"
"2: movq (%0), %%mm0\n"
" movntq %%mm0, (%1)\n"
" movq 8(%0), %%mm1\n"
" movntq %%mm1, 8(%1)\n"
" movq 16(%0), %%mm2\n"
" movntq %%mm2, 16(%1)\n"
" movq 24(%0), %%mm3\n"
" movntq %%mm3, 24(%1)\n"
" movq 32(%0), %%mm4\n"
" movntq %%mm4, 32(%1)\n"
" movq 40(%0), %%mm5\n"
" movntq %%mm5, 40(%1)\n"
" movq 48(%0), %%mm6\n"
" movntq %%mm6, 48(%1)\n"
" movq 56(%0), %%mm7\n"
" movntq %%mm7, 56(%1)\n"
".section .fixup, \"ax\"\n"
"3: movw $0x05EB, 1b\n" /* jmp on 5 bytes */
" jmp 2b\n"
".previous\n"
".section __ex_table,\"a\"\n"
" .align 4\n"
" .long 1b, 3b\n"
".previous"
: : "r" (from), "r" (to) : "memory");
from+=64;
to+=64;
}
--- cut the remainder ---
Also.. a while ago, there were some posts about a faster version. Does
anybody know why that version was never used?! (did nobody send a patch, or
was there something wrong with it?)
Message archive at:
http://www.ussg.iu.edu/hypermail/linux/kernel/0210.3/0156.html
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This archive was generated by hypermail 2b29 : Mon Jun 23 2003 - 22:00:32 EST