From: Eric Blake <eblake@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Alberto Garcia <berto@igalia.com>,
qemu-block@nongnu.org, Manos Pitsidianakis <el13635@mail.ntua.gr>,
Max Reitz <mreitz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3] throttle-groups: cancel timers on restart
Date: Mon, 25 Sep 2017 10:37:44 -0500 [thread overview]
Message-ID: <1d5203b2-dfb5-8eb0-4ff7-9ec2749e4317@redhat.com> (raw)
In-Reply-To: <20170925135735.25076-1-stefanha@redhat.com>
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On 09/25/2017 08:57 AM, Stefan Hajnoczi wrote:
> Throttling group members are restarted on config change and by
> bdrv_drained_begin(). Pending timers should be cancelled before
> restarting the queue, otherwise requests see that tg->any_timer_armed[]
> is already set and do not schedule a timer.
>
> For example, a hang occurs at least since QEMU 2.10.0 with -drive
> iops=100 because no further timers will be scheduled:
>
> (guest)$ dd if=/dev/zero of=/dev/vdb oflag=direct count=1000
> (qemu) stop
> (qemu) cont
> ...I/O is stuck...
>
> This can be fixed by calling throttle_group_detach_aio_context() from a
> bdrv_drained_begin/end() region. This way timers are quiesced properly,
> requests are drained, and other throttle group members are scheduled, if
> necessary.
>
> Reported-by: Yongxue Hong <yhong@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
Reviewed-by: Eric Blake <eblake@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
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next prev parent reply other threads:[~2017-09-25 15:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-25 13:57 [Qemu-devel] [PATCH v3] throttle-groups: cancel timers on restart Stefan Hajnoczi
2017-09-25 15:37 ` Eric Blake [this message]
2017-09-28 21:36 ` Alberto Garcia
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