67 lines
2.6 KiB
Diff
67 lines
2.6 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Fiona Ebner <f.ebner@proxmox.com>
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Date: Tue, 5 Dec 2023 14:05:49 +0100
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Subject: [PATCH] virtio blk/scsi: work around iothread polling getting stuck
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with drain
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When using iothread, after commits
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1665d9326f ("virtio-blk: implement BlockDevOps->drained_begin()")
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766aa2de0f ("virtio-scsi: implement BlockDevOps->drained_begin()")
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it can happen that polling gets stuck when draining. This would cause
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IO in the guest to get completely stuck.
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A workaround for users is stopping and resuming the vCPUs because that
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would also stop and resume the dataplanes which would kick the host
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notifiers.
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This can happen with block jobs like backup and drive mirror as well
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as with hotplug [2].
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Reports in the community forum that might be about this issue[0][1]
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and there is also one in the enterprise support channel.
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As a workaround in the code, just re-enable notifications and kick the
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virt queue after draining. Draining is already costly and rare, so no
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need to worry about a performance penalty here. This was taken from
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the following comment of a QEMU developer [3] (in my debugging,
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I had already found re-enabling notification to work around the issue,
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but also kicking the queue is more complete).
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[0]: https://forum.proxmox.com/threads/137286/
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[1]: https://forum.proxmox.com/threads/137536/
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[2]: https://issues.redhat.com/browse/RHEL-3934
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[3]: https://issues.redhat.com/browse/RHEL-3934?focusedId=23562096&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-23562096
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Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
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---
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hw/block/virtio-blk.c | 2 ++
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hw/scsi/virtio-scsi.c | 2 ++
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2 files changed, 4 insertions(+)
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diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
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index 39e7f23fab..22502047d5 100644
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--- a/hw/block/virtio-blk.c
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+++ b/hw/block/virtio-blk.c
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@@ -1537,6 +1537,8 @@ static void virtio_blk_drained_end(void *opaque)
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for (uint16_t i = 0; i < s->conf.num_queues; i++) {
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VirtQueue *vq = virtio_get_queue(vdev, i);
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virtio_queue_aio_attach_host_notifier(vq, ctx);
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+ virtio_queue_set_notification(vq, 1);
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+ virtio_queue_notify(vdev, i);
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}
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}
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diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
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index 45b95ea070..a7bddbf899 100644
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--- a/hw/scsi/virtio-scsi.c
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+++ b/hw/scsi/virtio-scsi.c
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@@ -1166,6 +1166,8 @@ static void virtio_scsi_drained_end(SCSIBus *bus)
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for (uint32_t i = 0; i < total_queues; i++) {
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VirtQueue *vq = virtio_get_queue(vdev, i);
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virtio_queue_aio_attach_host_notifier(vq, s->ctx);
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+ virtio_queue_set_notification(vq, 1);
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+ virtio_queue_notify(vdev, i);
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}
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}
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