Messages in this thread | | | Date | Thu, 06 Sep 2018 20:18:11 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v36 0/5] Virtio-balloon: support free page reporting |
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On 07/23/2018 10:36 PM, Dr. David Alan Gilbert wrote: > * Michael S. Tsirkin (mst@redhat.com) wrote: >> On Fri, Jul 20, 2018 at 04:33:00PM +0800, Wei Wang wrote: >>> This patch series is separated from the previous "Virtio-balloon >>> Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT, >>> implemented by this series enables the virtio-balloon driver to report >>> hints of guest free pages to the host. It can be used to accelerate live >>> migration of VMs. Here is an introduction of this usage: >>> >>> Live migration needs to transfer the VM's memory from the source machine >>> to the destination round by round. For the 1st round, all the VM's memory >>> is transferred. From the 2nd round, only the pieces of memory that were >>> written by the guest (after the 1st round) are transferred. One method >>> that is popularly used by the hypervisor to track which part of memory is >>> written is to write-protect all the guest memory. >>> >>> This feature enables the optimization by skipping the transfer of guest >>> free pages during VM live migration. It is not concerned that the memory >>> pages are used after they are given to the hypervisor as a hint of the >>> free pages, because they will be tracked by the hypervisor and transferred >>> in the subsequent round if they are used and written. >>> >>> * Tests >>> - Test Environment >>> Host: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz >>> Guest: 8G RAM, 4 vCPU >>> Migration setup: migrate_set_speed 100G, migrate_set_downtime 2 second >>> >>> - Test Results >>> - Idle Guest Live Migration Time (results are averaged over 10 runs): >>> - Optimization v.s. Legacy = 409ms vs 1757ms --> ~77% reduction >>> (setting page poisoning zero and enabling ksm don't affect the >>> comparison result) >>> - Guest with Linux Compilation Workload (make bzImage -j4): >>> - Live Migration Time (average) >>> Optimization v.s. Legacy = 1407ms v.s. 2528ms --> ~44% reduction >>> - Linux Compilation Time >>> Optimization v.s. Legacy = 5min4s v.s. 5min12s >>> --> no obvious difference >> I'd like to see dgilbert's take on whether this kind of gain >> justifies adding a PV interfaces, and what kind of guest workload >> is appropriate. >> >> Cc'd. > Well, 44% is great ... although the measurement is a bit weird. > > a) A 2 second downtime is very large; 300-500ms is more normal > b) I'm not sure what the 'average' is - is that just between a bunch of > repeated migrations? > c) What load was running in the guest during the live migration? > > An interesting measurement to add would be to do the same test but > with a VM with a lot more RAM but the same load; you'd hope the gain > would be even better. > It would be interesting, especially because the users who are interested > are people creating VMs allocated with lots of extra memory (for the > worst case) but most of the time migrating when it's fairly idle. > > Dave >
Hi Dave,
The results of the added experiments have been shown in the v37 cover letter. Could you have a look at https://lkml.org/lkml/2018/8/27/29 . Thanks.
Best, Wei
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