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authorFam Zheng <famz@redhat.com>2016-03-01 14:18:24 +0800
committerPaolo Bonzini <pbonzini@redhat.com>2016-03-07 13:26:37 +0100
commit729633c2bc30496073431584eb6e304776b4ebd4 (patch)
treea6147327b26ce18f8aa80b5e50093896a68f2ac7 /exec.c
parent29cb533d8cbff1330717619780c2f1dfe764e003 (diff)
downloadqemu-arm-729633c2bc30496073431584eb6e304776b4ebd4.tar.gz
exec: Introduce AddressSpaceDispatch.mru_section
Under heavy workloads the lookup will likely end up with the same MemoryRegionSection from last time. Using a pointer to cache the result, like ram_list.mru_block, significantly reduces cost of address_space_translate. During address space topology update, as->dispatch will be reallocated so the pointer is invalidated automatically. Perf reports a visible drop on the cpu usage, because phys_page_find is not called. Before: 2.35% qemu-system-x86_64 [.] phys_page_find 0.97% qemu-system-x86_64 [.] address_space_translate_internal 0.95% qemu-system-x86_64 [.] address_space_translate 0.55% qemu-system-x86_64 [.] address_space_lookup_region After: 0.97% qemu-system-x86_64 [.] address_space_translate_internal 0.97% qemu-system-x86_64 [.] address_space_lookup_region 0.84% qemu-system-x86_64 [.] address_space_translate Signed-off-by: Fam Zheng <famz@redhat.com> Message-Id: <1456813104-25902-8-git-send-email-famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'exec.c')
-rw-r--r--exec.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/exec.c b/exec.c
index 9279af5eab..f09dd4e928 100644
--- a/exec.c
+++ b/exec.c
@@ -135,6 +135,7 @@ typedef struct PhysPageMap {
struct AddressSpaceDispatch {
struct rcu_head rcu;
+ MemoryRegionSection *mru_section;
/* This is a multi-level map on the physical address space.
* The bottom level has pointers to MemoryRegionSections.
*/
@@ -351,14 +352,25 @@ static MemoryRegionSection *address_space_lookup_region(AddressSpaceDispatch *d,
hwaddr addr,
bool resolve_subpage)
{
- MemoryRegionSection *section;
+ MemoryRegionSection *section = atomic_read(&d->mru_section);
subpage_t *subpage;
+ bool update;
- section = phys_page_find(d->phys_map, addr, d->map.nodes, d->map.sections);
+ if (section && section != &d->map.sections[PHYS_SECTION_UNASSIGNED] &&
+ section_covers_addr(section, addr)) {
+ update = false;
+ } else {
+ section = phys_page_find(d->phys_map, addr, d->map.nodes,
+ d->map.sections);
+ update = true;
+ }
if (resolve_subpage && section->mr->subpage) {
subpage = container_of(section->mr, subpage_t, iomem);
section = &d->map.sections[subpage->sub_section[SUBPAGE_IDX(addr)]];
}
+ if (update) {
+ atomic_set(&d->mru_section, section);
+ }
return section;
}