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c5cd7e5f23
On setups with one or more virtio-net devices with vhost on, dirty tracking iteration increases cost the bigger the number amount of queues are set up e.g. on idle guests migration the following is observed with virtio-net with vhost=on: 48 queues -> 78.11% [.] vhost_dev_sync_region.isra.13 8 queues -> 40.50% [.] vhost_dev_sync_region.isra.13 1 queue -> 6.89% [.] vhost_dev_sync_region.isra.13 2 devices, 1 queue -> 18.60% [.] vhost_dev_sync_region.isra.14 With high memory rates the symptom is lack of convergence as soon as it has a vhost device with a sufficiently high number of queues, the sufficient number of vhost devices. On every migration iteration (every 100msecs) it will redundantly query the *shared log* the number of queues configured with vhost that exist in the guest. For the virtqueue data, this is necessary, but not for the memory sections which are the same. So essentially we end up scanning the dirty log too often. To fix that, select a vhost device responsible for scanning the log with regards to memory sections dirty tracking. It is selected when we enable the logger (during migration) and cleared when we disable the logger. If the vhost logger device goes away for some reason, the logger will be re-selected from the rest of vhost devices. After making mem-section logger a singleton instance, constant cost of 7%-9% (like the 1 queue report) will be seen, no matter how many queues or how many vhost devices are configured: 48 queues -> 8.71% [.] vhost_dev_sync_region.isra.13 2 devices, 8 queues -> 7.97% [.] vhost_dev_sync_region.isra.14 Co-developed-by: Joao Martins <joao.m.martins@oracle.com> Signed-off-by: Joao Martins <joao.m.martins@oracle.com> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com> Message-Id: <1710448055-11709-2-git-send-email-si-wei.liu@oracle.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Jason Wang <jasowang@redhat.com> |
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| qemu-io.h | ||
| qemu-main.h | ||