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Optimize out a TLB invalidation in a common case of pmap_enter(): if 

the PTE was previously invalid, no TLB invalidation is necessary because:

	(1) when a PTE is invalidated, its entry is flushed from the
	    TLB

	(2) the PALcode won't install an invalid PTE into the TLB.
This commit is contained in:
thorpej 1998-03-18 22:13:58 +00:00
parent e14a1c1120
commit 605472f676
1 changed files with 16 additions and 5 deletions
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21
sys/arch/alpha/alpha/pmap.old.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: pmap.old.c,v 1.60 1998/03/18 21:57:03 thorpej Exp $ */
/* $NetBSD: pmap.old.c,v 1.61 1998/03/18 22:13:58 thorpej Exp $ */
/*-
* Copyright (c) 1998 The NetBSD Foundation, Inc.
@ -155,7 +155,7 @@
#include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
__KERNEL_RCSID(0, "$NetBSD: pmap.old.c,v 1.60 1998/03/18 21:57:03 thorpej Exp $");
__KERNEL_RCSID(0, "$NetBSD: pmap.old.c,v 1.61 1998/03/18 22:13:58 thorpej Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@ -1165,7 +1165,7 @@ pmap_enter(pmap, va, pa, prot, wired)
boolean_t managed;
pt_entry_t *pte, npte;
vm_offset_t opa;
boolean_t wiring_only = FALSE;
boolean_t tflush = TRUE;
#ifdef DEBUG
if (pmapdebug & (PDB_FOLLOW|PDB_ENTER))
@ -1267,6 +1267,13 @@ pmap_enter(pmap, va, pa, prot, wired)
* new one immediately.
*/
if (pmap_pte_v(pte) == 0) {
/*
* No need to invalidate the TLB in this case; an invalid
* mapping won't be in the TLB, and a previously valid
* mapping would have been flushed when it was invalidated.
*/
tflush = FALSE;
if (pmap != pmap_kernel()) {
/*
* New mappings gain a reference on the level 3
@ -1305,7 +1312,11 @@ pmap_enter(pmap, va, pa, prot, wired)
* change.
*/
if (pmap_pte_prot(pte) == pte_prot(pmap, prot)) {
wiring_only = TRUE;
/*
* Wiring-only changes only affect software
* PTE bits; no TLB invalidation is necessary.
*/
tflush = FALSE;
#ifdef PMAPSTATS
enter_stats.wchange++;
#endif
@ -1400,7 +1411,7 @@ pmap_enter(pmap, va, pa, prot, wired)
* caches. Note that this is not necessary for wiring-only
* changes.
*/
if (wiring_only == FALSE && active_pmap(pmap)) {
if (tflush && active_pmap(pmap)) {
ALPHA_TBIS(va);
if (prot & VM_PROT_EXECUTE)
alpha_pal_imb();