From: Peter Xu <email@example.com> To: firstname.lastname@example.org, email@example.com Cc: Paolo Bonzini <firstname.lastname@example.org>, Vitaly Kuznetsov <email@example.com>, Maxim Levitsky <firstname.lastname@example.org>, email@example.com, Sean Christopherson <firstname.lastname@example.org> Subject: [PATCH 0/9] KVM: X86: Some light optimizations on rmap logic Date: Thu, 24 Jun 2021 14:13:47 -0400 [thread overview] Message-ID: <email@example.com> (raw) (This is still based on a random 5.13-rc3-ish branch, but I can rebase if needed)\r \r All things started from patch 1, which introduced a new statistic to keep "max\r rmap entry count per vm". At that time I was just curious about how many rmap\r is there normally for a guest, and it surprised me a bit.\r \r For TDP mappings it's all fine as mostly rmap of a page is either 0 or 1\r depending on faulted or not. It turns out with EPT=N there seems to be a huge\r number of pages that can have tens or hundreds of rmap entries even for an idle\r guest. Then I continued with the rest.\r \r To understand better on "how much of those pages", I did patch 2-6 which\r introduced the idea of per-arch per-vm debugfs nodes, and added a debug file to\r do statistics for rmap, which is similar to kvm_arch_create_vcpu_debugfs() but\r for vm not vcpu.\r \r I did notice this should be the clean approach as I also see other archs\r randomly create some per-vm debugfs nodes there:\r \r ---8<---\r *** arch/arm64/kvm/vgic/vgic-debug.c:\r vgic_debug_init debugfs_create_file("vgic-state", 0444, kvm->debugfs_dentry, kvm,\r \r *** arch/powerpc/kvm/book3s_64_mmu_hv.c:\r kvmppc_mmu_debugfs_init debugfs_create_file("htab", 0400, kvm->arch.debugfs_dir, kvm,\r \r *** arch/powerpc/kvm/book3s_64_mmu_radix.c:\r kvmhv_radix_debugfs_init debugfs_create_file("radix", 0400, kvm->arch.debugfs_dir, kvm,\r \r *** arch/powerpc/kvm/book3s_hv.c:\r debugfs_vcpu_init debugfs_create_file("timings", 0444, vcpu->arch.debugfs_dir, vcpu,\r \r *** arch/powerpc/kvm/book3s_xics.c:\r xics_debugfs_init xics->dentry = debugfs_create_file(name, 0444, powerpc_debugfs_root,\r \r *** arch/powerpc/kvm/book3s_xive.c:\r xive_debugfs_init xive->dentry = debugfs_create_file(name, S_IRUGO, powerpc_debugfs_root,\r \r *** arch/powerpc/kvm/timing.c:\r kvmppc_create_vcpu_debugfs debugfs_file = debugfs_create_file(dbg_fname, 0666, kvm_debugfs_dir,\r ---8<---\r \r PPC even has its own per-vm dir for that. I think if patch 2-6 can be\r considered to be accepted then the next thing to consider is to merge all these\r usages to be under the same existing per-vm dentry with their per-arch hooks\r introduced.\r \r The last 3 patches (patch 7-9) are a few optimizations of existing rmap logic.\r The major test case I used is rmap_fork , however it's not really the ideal\r one to show their effect for sure as that test I wrote covers both\r rmap_add/remove, while I don't have good idea on optimizing rmap_remove without\r changing the array structure or adding much overhead (e.g. sort the array, or\r making a tree-like structure somehow to replace the array list). However it\r already shows some benefit with those changes, so I post them out.\r \r Applying patch 7-8 will bring a summary of 38% perf boost when I fork 500\r childs with the test I used. Didn't run perf test on patch 9. More in the\r commit log.\r \r Please review, thanks.\r \r  https://github.com/xzpeter/clibs/commit/825436f825453de2ea5aaee4bdb1c92281efe5b3\r \r Peter Xu (9):\r KVM: X86: Add per-vm stat for max rmap list size\r KVM: Introduce kvm_get_kvm_safe()\r KVM: Allow to have arch-specific per-vm debugfs files\r KVM: X86: Introduce pte_list_count() helper\r KVM: X86: Introduce kvm_mmu_slot_lpages() helpers\r KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file\r KVM: X86: MMU: Tune PTE_LIST_EXT to be bigger\r KVM: X86: Optimize pte_list_desc with per-array counter\r KVM: X86: Optimize zapping rmap\r \r arch/x86/include/asm/kvm_host.h | 1 +\r arch/x86/kvm/mmu/mmu.c | 90 +++++++++++++++++-----\r arch/x86/kvm/mmu/mmu_internal.h | 1 +\r arch/x86/kvm/x86.c | 131 +++++++++++++++++++++++++++++++-\r include/linux/kvm_host.h | 2 +\r virt/kvm/kvm_main.c | 36 +++++++--\r 6 files changed, 233 insertions(+), 28 deletions(-)\r \r -- \r 2.31.1\r \r
next reply other threads:[~2021-06-24 18:14 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-24 18:13 Peter Xu [this message] 2021-06-24 18:13 ` [PATCH 1/9] KVM: X86: Add per-vm stat for max rmap list size Peter Xu 2021-06-24 18:13 ` [PATCH 2/9] KVM: Introduce kvm_get_kvm_safe() Peter Xu 2021-06-24 18:13 ` [PATCH 3/9] KVM: Allow to have arch-specific per-vm debugfs files Peter Xu 2021-06-24 18:13 ` [PATCH 4/9] KVM: X86: Introduce pte_list_count() helper Peter Xu 2021-06-24 18:13 ` [PATCH 5/9] KVM: X86: Introduce kvm_mmu_slot_lpages() helpers Peter Xu 2021-06-24 18:13 ` [PATCH 6/9] KVM: X86: Introduce mmu_rmaps_stat per-vm debugfs file Peter Xu 2021-06-24 18:22 ` Peter Xu 2021-06-24 18:13 ` [PATCH 7/9] KVM: X86: MMU: Tune PTE_LIST_EXT to be bigger Peter Xu 2021-06-24 18:15 ` [PATCH 8/9] KVM: X86: Optimize pte_list_desc with per-array counter Peter Xu 2021-06-24 22:53 ` Peter Xu 2021-06-24 18:15 ` [PATCH 9/9] KVM: X86: Optimize zapping rmap Peter Xu
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