From 729633c2bc30496073431584eb6e304776b4ebd4 Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Tue, 1 Mar 2016 14:18:24 +0800 Subject: [PATCH] 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 Message-Id: <1456813104-25902-8-git-send-email-famz@redhat.com> Signed-off-by: Paolo Bonzini --- exec.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/exec.c b/exec.c index 9279af5..f09dd4e 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; } -- 2.7.4