Author: alc
Date: Wed Mar 2 00:24:07 2011
New Revision: 219157
URL: http://svn.freebsd.org/changeset/base/219157
Log:
Make a change to the implementation of the direct map to improve performance
on processors that support 1 GB pages. Specifically, if the end of physical
memory is not aligned to a 1 GB page boundary, then map the residual
physical memory with multiple 2 MB page mappings rather than a single 1 GB
page mapping. When a 1 GB page mapping is used for this residual memory,
access to the memory is slower than when multiple 2 MB page mappings are
used. (I suspect that the reason for this slowdown is that the TLB is
actually being loaded with 4 KB page mappings for the residual memory.)
X-MFC after: r214425
Modified:
head/sys/amd64/amd64/pmap.c
Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c Tue Mar 1 21:52:24 2011 (r219156)
+++ head/sys/amd64/amd64/pmap.c Wed Mar 2 00:24:07 2011 (r219157)
@@ -457,7 +457,7 @@ CTASSERT(powerof2(NDMPML4E));
static void
create_pagetables(vm_paddr_t *firstaddr)
{
- int i;
+ int i, j, ndm1g;
/* Allocate pages */
KPTphys = allocpages(firstaddr, NKPT);
@@ -469,8 +469,11 @@ create_pagetables(vm_paddr_t *firstaddr)
if (ndmpdp < 4) /* Minimum 4GB of dirmap */
ndmpdp = 4;
DMPDPphys = allocpages(firstaddr, NDMPML4E);
- if ((amd_feature & AMDID_PAGE1GB) == 0)
- DMPDphys = allocpages(firstaddr, ndmpdp);
+ ndm1g = 0;
+ if ((amd_feature & AMDID_PAGE1GB) != 0)
+ ndm1g = ptoa(Maxmem) >> PDPSHIFT;
+ if (ndm1g < ndmpdp)
+ DMPDphys = allocpages(firstaddr, ndmpdp - ndm1g);
dmaplimit = (vm_paddr_t)ndmpdp << PDPSHIFT;
/* Fill in the underlying page table pages */
@@ -502,32 +505,28 @@ create_pagetables(vm_paddr_t *firstaddr)
}
/*
- * Now, set up the direct map region using either 2MB or 1GB pages.
- * Later, if pmap_mapdev{_attr}() uses the direct map for non-write-
- * back memory, pmap_change_attr() will demote any 2MB or 1GB page
- * mappings that are partially used.
- */
- if ((amd_feature & AMDID_PAGE1GB) == 0) {
- for (i = 0; i < NPDEPG * ndmpdp; i++) {
- ((pd_entry_t *)DMPDphys)[i] = (vm_paddr_t)i << PDRSHIFT;
- /* Preset PG_M and PG_A because demotion expects it. */
- ((pd_entry_t *)DMPDphys)[i] |= PG_RW | PG_V | PG_PS |
- PG_G | PG_M | PG_A;
- }
- /* And the direct map space's PDP */
- for (i = 0; i < ndmpdp; i++) {
- ((pdp_entry_t *)DMPDPphys)[i] = DMPDphys +
- (i << PAGE_SHIFT);
- ((pdp_entry_t *)DMPDPphys)[i] |= PG_RW | PG_V | PG_U;
- }
- } else {
- for (i = 0; i < ndmpdp; i++) {
- ((pdp_entry_t *)DMPDPphys)[i] =
- (vm_paddr_t)i << PDPSHIFT;
- /* Preset PG_M and PG_A because demotion expects it. */
- ((pdp_entry_t *)DMPDPphys)[i] |= PG_RW | PG_V | PG_PS |
- PG_G | PG_M | PG_A;
- }
+ * Now, set up the direct map region using 2MB and/or 1GB pages. If
+ * the end of physical memory is not aligned to a 1GB page boundary,
+ * then the residual physical memory is mapped with 2MB pages. Later,
+ * if pmap_mapdev{_attr}() uses the direct map for non-write-back
+ * memory, pmap_change_attr() will demote any 2MB or 1GB page mappings
+ * that are partially used.
+ */
+ for (i = NPDEPG * ndm1g, j = 0; i < NPDEPG * ndmpdp; i++, j++) {
+ ((pd_entry_t *)DMPDphys)[j] = (vm_paddr_t)i << PDRSHIFT;
+ /* Preset PG_M and PG_A because demotion expects it. */
+ ((pd_entry_t *)DMPDphys)[j] |= PG_RW | PG_V | PG_PS | PG_G |
+ PG_M | PG_A;
+ }
+ for (i = 0; i < ndm1g; i++) {
+ ((pdp_entry_t *)DMPDPphys)[i] = (vm_paddr_t)i << PDPSHIFT;
+ /* Preset PG_M and PG_A because demotion expects it. */
+ ((pdp_entry_t *)DMPDPphys)[i] |= PG_RW | PG_V | PG_PS | PG_G |
+ PG_M | PG_A;
+ }
+ for (j = 0; i < ndmpdp; i++, j++) {
+ ((pdp_entry_t *)DMPDPphys)[i] = DMPDphys + (j << PAGE_SHIFT);
+ ((pdp_entry_t *)DMPDPphys)[i] |= PG_RW | PG_V | PG_U;
}
/* And recursively map PML4 to itself in order to get PTmap */
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