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Date: Thu, 28 May 2015 13:19:08 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v6 01/13] block: Add op blocker type
 "device IO"
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To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, armbru@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, amit.shah@redhat.com



On 28/05/2015 13:11, Fam Zheng wrote:
> > Whoever uses ioeventfd needs to implement pause/resume, yes---not just
> > dataplane, also "regular" virtio-blk/virtio-scsi.
> > 
> > However, everyone else should be okay, because the bottom half runs
> > immediately and the big QEMU lock is not released in the meanwhile.  So
> > the CPUs have no occasion to run.  This needs a comment!
> 
> I'm not sure. It seems timer callbacks also do I/O, for example
> nvme_process_sq().

Right, that's also true for USB devices. :(

Perhaps we can skip block_job_defer_to_main_loop if not necessary
(bs->aio_context == qemu_get_aio_context()).

Paolo