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Make a change to the implementation of the direct map to improve performance

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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
This commit is contained in:
Alan Cox 2011-03-02 00:24:07 +00:00
parent 3658c9776e
commit cb25117d54
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=219157
1 changed files with 27 additions and 28 deletions
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55
sys/amd64/amd64/pmap.c
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@ -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.
* 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.
*/
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;
}
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 */