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[Qemu-commits] [qemu/qemu] 75dcb4: virtio-blk: fix host notifier issues
From: |
Richard Henderson |
Subject: |
[Qemu-commits] [qemu/qemu] 75dcb4: virtio-blk: fix host notifier issues during datapl... |
Date: |
Wed, 12 Jul 2023 12:46:43 -0700 |
Branch: refs/heads/staging
Home: https://github.com/qemu/qemu
Commit: 75dcb4d790bbe5327169fd72b185960ca58e2fa6
https://github.com/qemu/qemu/commit/75dcb4d790bbe5327169fd72b185960ca58e2fa6
Author: Stefan Hajnoczi <stefanha@redhat.com>
Date: 2023-07-12 (Wed, 12 Jul 2023)
Changed paths:
M hw/block/dataplane/virtio-blk.c
Log Message:
-----------
virtio-blk: fix host notifier issues during dataplane start/stop
The main loop thread can consume 100% CPU when using --device
virtio-blk-pci,iothread=<iothread>. ppoll() constantly returns but
reading virtqueue host notifiers fails with EAGAIN. The file descriptors
are stale and remain registered with the AioContext because of bugs in
the virtio-blk dataplane start/stop code.
The problem is that the dataplane start/stop code involves drain
operations, which call virtio_blk_drained_begin() and
virtio_blk_drained_end() at points where the host notifier is not
operational:
- In virtio_blk_data_plane_start(), blk_set_aio_context() drains after
vblk->dataplane_started has been set to true but the host notifier has
not been attached yet.
- In virtio_blk_data_plane_stop(), blk_drain() and blk_set_aio_context()
drain after the host notifier has already been detached but with
vblk->dataplane_started still set to true.
I would like to simplify ->ioeventfd_start/stop() to avoid interactions
with drain entirely, but couldn't find a way to do that. Instead, this
patch accepts the fragile nature of the code and reorders it so that
vblk->dataplane_started is false during drain operations. This way the
virtio_blk_drained_begin() and virtio_blk_drained_end() calls don't
touch the host notifier. The result is that
virtio_blk_data_plane_start() and virtio_blk_data_plane_stop() have
complete control over the host notifier and stale file descriptors are
no longer left in the AioContext.
This patch fixes the 100% CPU consumption in the main loop thread and
correctly moves host notifier processing to the IOThread.
Fixes: 1665d9326fd2 ("virtio-blk: implement BlockDevOps->drained_begin()")
Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Lukas Doktor <ldoktor@redhat.com>
Message-id: 20230704151527.193586-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Commit: 3dd9e54703e6ae4f9ab3767f5cecc99edf066668
https://github.com/qemu/qemu/commit/3dd9e54703e6ae4f9ab3767f5cecc99edf066668
Author: Richard Henderson <richard.henderson@linaro.org>
Date: 2023-07-12 (Wed, 12 Jul 2023)
Changed paths:
M hw/block/dataplane/virtio-blk.c
Log Message:
-----------
Merge tag 'block-pull-request' of https://gitlab.com/stefanha/qemu into
staging
Pull request
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# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg: aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
* tag 'block-pull-request' of https://gitlab.com/stefanha/qemu:
virtio-blk: fix host notifier issues during dataplane start/stop
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Compare: https://github.com/qemu/qemu/compare/6f05a92ddc73...3dd9e54703e6
- [Qemu-commits] [qemu/qemu] 75dcb4: virtio-blk: fix host notifier issues during datapl...,
Richard Henderson <=