From: Paolo Bonzini <pbonzini@redhat.com> To: Xiao Guangrong <guangrong.xiao@gmail.com>, mtosatti@redhat.com, avi.kivity@gmail.com, rkrcmar@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Xiao Guangrong <xiaoguangrong@tencent.com> Subject: Re: [PATCH 0/7] KVM: MMU: fast write protect Date: Wed, 3 May 2017 16:57:19 +0200 [thread overview] Message-ID: <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> (raw) In-Reply-To: <ff732c49-de24-eebd-ae8e-2de00281f211@gmail.com> On 03/05/2017 16:50, Xiao Guangrong wrote: > Furthermore, userspace has no knowledge about if PML is enable (it > can be required from sysfs, but it is a good way in QEMU), so it is > difficult for the usespace to know when to use write-protect-all. > Maybe we can make KVM_CAP_X86_WRITE_PROTECT_ALL_MEM return false if > PML is enabled? Yes, that's a good idea. Though it's a pity that, with PML, setting the dirty bit will still do the massive walk of the rmap. At least with reset_dirty_pages it's done a little bit at a time. >> Also, I wonder how the alternative write protection mechanism would >> affect performance of the dirty page ring buffer patches. You would do >> the write protection of all memory at the end of >> kvm_vm_ioctl_reset_dirty_pages. You wouldn't even need a separate >> ioctl, which is nice. On the other hand, checkpoints would be more >> frequent and most pages would be write-protected, so it would be more >> expensive to rebuild the shadow page tables... > > Yup, write-protect-all can improve reset_dirty_pages indeed, i will > apply your idea after reset_dirty_pages is merged. > > However, we still prefer to have a separate ioctl for write-protect-all > which cooperates with KVM_GET_DIRTY_LOG to improve live migration that > should not always depend on checkpoint. Ok, I plan to merge the dirty ring pages early in 4.13 development. Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com> To: Xiao Guangrong <guangrong.xiao@gmail.com>, mtosatti@redhat.com, avi.kivity@gmail.com, rkrcmar@redhat.com Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, Xiao Guangrong <xiaoguangrong@tencent.com> Subject: Re: [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect Date: Wed, 3 May 2017 16:57:19 +0200 [thread overview] Message-ID: <878cbc47-316c-d508-a5a3-22029dee2203@redhat.com> (raw) In-Reply-To: <ff732c49-de24-eebd-ae8e-2de00281f211@gmail.com> On 03/05/2017 16:50, Xiao Guangrong wrote: > Furthermore, userspace has no knowledge about if PML is enable (it > can be required from sysfs, but it is a good way in QEMU), so it is > difficult for the usespace to know when to use write-protect-all. > Maybe we can make KVM_CAP_X86_WRITE_PROTECT_ALL_MEM return false if > PML is enabled? Yes, that's a good idea. Though it's a pity that, with PML, setting the dirty bit will still do the massive walk of the rmap. At least with reset_dirty_pages it's done a little bit at a time. >> Also, I wonder how the alternative write protection mechanism would >> affect performance of the dirty page ring buffer patches. You would do >> the write protection of all memory at the end of >> kvm_vm_ioctl_reset_dirty_pages. You wouldn't even need a separate >> ioctl, which is nice. On the other hand, checkpoints would be more >> frequent and most pages would be write-protected, so it would be more >> expensive to rebuild the shadow page tables... > > Yup, write-protect-all can improve reset_dirty_pages indeed, i will > apply your idea after reset_dirty_pages is merged. > > However, we still prefer to have a separate ioctl for write-protect-all > which cooperates with KVM_GET_DIRTY_LOG to improve live migration that > should not always depend on checkpoint. Ok, I plan to merge the dirty ring pages early in 4.13 development. Paolo
next prev parent reply other threads:[~2017-05-03 14:57 UTC|newest] Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-05-03 10:52 [PATCH 0/7] KVM: MMU: fast write protect guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 1/7] KVM: MMU: correct the behavior of mmu_spte_update_no_track guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 2/7] KVM: MMU: introduce possible_writable_spte_bitmap guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 3/7] KVM: MMU: introduce kvm_mmu_write_protect_all_pages guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 4/7] KVM: MMU: enable KVM_WRITE_PROTECT_ALL_MEM guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 5/7] KVM: MMU: allow dirty log without write protect guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 6/7] KVM: MMU: clarify fast_pf_fix_direct_spte guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 10:52 ` [PATCH 7/7] KVM: MMU: stop using mmu_spte_get_lockless under mmu-lock guangrong.xiao 2017-05-03 10:52 ` [Qemu-devel] " guangrong.xiao 2017-05-03 12:28 ` [PATCH 0/7] KVM: MMU: fast write protect Paolo Bonzini 2017-05-03 12:28 ` [Qemu-devel] " Paolo Bonzini 2017-05-03 14:50 ` Xiao Guangrong 2017-05-03 14:50 ` [Qemu-devel] " Xiao Guangrong 2017-05-03 14:57 ` Paolo Bonzini [this message] 2017-05-03 14:57 ` Paolo Bonzini 2017-05-04 3:36 ` Xiao Guangrong 2017-05-04 3:36 ` [Qemu-devel] " Xiao Guangrong 2017-05-04 7:06 ` Paolo Bonzini 2017-05-04 7:06 ` [Qemu-devel] " Paolo Bonzini 2017-05-23 2:23 ` Xiao Guangrong 2017-05-23 2:23 ` [Qemu-devel] " Xiao Guangrong 2017-05-29 16:48 ` Paolo Bonzini 2017-05-29 16:48 ` [Qemu-devel] " Paolo Bonzini 2017-06-09 3:19 ` Xiao Guangrong 2017-06-09 3:19 ` [Qemu-devel] " Xiao Guangrong 2017-06-05 7:36 ` Jay Zhou 2017-06-05 7:36 ` Jay Zhou 2017-06-06 2:56 ` Xiao Guangrong
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