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From: Peter Wemm <peter@FreeBSD.org>
To: Perforce Change Reviews <perforce@freebsd.org>
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Subject: PERFORCE change 93334 for review
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http://perforce.freebsd.org/chv.cgi?CH=93334

Change 93334 by peter@peter_melody on 2006/03/15 02:31:50

	Instead of iterating through the loop 160 times, use a while
	loop to examine each of the three bitmaps and the cpu's built
	in bsfq instruction (like ffs()).  This is why I wanted to
	kill the sva/eva option, because the bit scan instructions do
	not have an easy way of skipping or ignoring bits.

Affected files ...

.. //depot/projects/hammer/sys/amd64/amd64/pmap.c#142 edit

Differences ...

==== //depot/projects/hammer/sys/amd64/amd64/pmap.c#142 (text+ko) ====

@@ -1451,6 +1451,8 @@
 #define	PC_FREE1	0xfffffffffffffffful
 #define	PC_FREE2	0x000000fffffffffful
 
+static uint64_t pc_freemask[3] = { PC_FREE0, PC_FREE1, PC_FREE2 };
+
 static int pc_chunk_count, pc_chunk_allocs, pc_chunk_frees;
 
 SYSCTL_INT(_vm_pmap, OID_AUTO, pc_chunk_count, CTLFLAG_RD, &pc_chunk_count, 0,
@@ -2692,6 +2694,7 @@
 	struct pv_chunk *pc, *npc;
 	int field, idx;
 	int64_t bit;
+	uint64_t inuse;
 
 	if (pmap != vmspace_pmap(curthread->td_proc->p_vmspace)) {
 		printf("warning: pmap_remove_pages called with non-current pmap\n");
@@ -2706,10 +2709,10 @@
 		 * the for loop.  Since we free as we go, we won't have
 		 * to skip unfreeable ones that sva/eva might have allowed.
 		 */
-		for (idx = 0; idx < _NPCPV; idx++) {
-			field = idx / 64;
-			bit = idx % 64;
-			if ((pc->pc_map[field] & 1ul << bit) == 0) { /* inuse */
+		for (field = 0; field < _NPCM; field++) {
+			while ((inuse = (~(pc->pc_map[field])) & pc_freemask[field]) != 0) {
+				bit = bsfq(inuse);
+				idx = field * 64 + bit;
 				pv = &pc->pc_pventry[idx];
 
 				pte = vtopte(pv->pv_va);