[pve-devel] applied-series: [PATCH qemu 1/2] add patch to work around stuck guest IO with iothread and VirtIO block/SCSI

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Am 11/12/2023 um 14:28 schrieb Fiona Ebner:
> When using iothread, after commits
> 1665d9326f ("virtio-blk: implement BlockDevOps->drained_begin()")
> 766aa2de0f ("virtio-scsi: implement BlockDevOps->drained_begin()")
> it can happen that polling gets stuck when draining. This would cause
> IO in the guest to get completely stuck.
> 
> A workaround for users is stopping and resuming the vCPUs because that
> would also stop and resume the dataplanes which would kick the host
> notifiers.
> 
> This can happen with block jobs like backup and drive mirror as well
> as with hotplug [2].
> 
> Reports in the community forum that might be about this issue[0][1]
> and there is also one in the enterprise support channel.
> 
> As a workaround in the code, just re-enable notifications and kick the
> virt queue after draining. Draining is already costly and rare, so no
> need to worry about a performance penalty here. This was taken from
> the following comment of a QEMU developer [3] (in my debugging,
> I had already found re-enabling notification to work around the issue,
> but also kicking the queue is more complete).
> 
> [0]: https://forum.proxmox.com/threads/137286/
> [1]: https://forum.proxmox.com/threads/137536/
> [2]: https://issues.redhat.com/browse/RHEL-3934
> [3]: https://issues.redhat.com/browse/RHEL-3934?focusedId=23562096&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-23562096
> 
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
> ---
>  ...work-around-iothread-polling-getting.patch | 66 +++++++++++++++++++
>  debian/patches/series                         |  1 +
>  2 files changed, 67 insertions(+)
>  create mode 100644 debian/patches/pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch
> 
>

applied both patches, thanks!