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author | Fam Zheng <famz@redhat.com> | 2016-03-01 14:18:24 +0800 |
---|---|---|
committer | Timothy Pearson <tpearson@raptorengineering.com> | 2019-11-29 19:49:12 -0600 |
commit | b527bb9200ccaaf0afcc83c13a34ee7bf2d28438 (patch) | |
tree | 2285e7770378832466798031b167e6f4c73c0528 | |
parent | 74f8e4eb79703798d61775c6b3df40ba700b5916 (diff) | |
download | hqemu-b527bb9200ccaaf0afcc83c13a34ee7bf2d28438.zip hqemu-b527bb9200ccaaf0afcc83c13a34ee7bf2d28438.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>
-rw-r--r-- | exec.c | 16 |
1 files changed, 14 insertions, 2 deletions
@@ -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; } |