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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 23 May 2016 10:17:45 +0200
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Subject: Re: [Qemu-devel] [PATCH 5/9] virtio-blk: multiqueue batch notify
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To: Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Ming Lei <ming.lei@canonical.com>, qemu-devel@nongnu.org



On 23/05/2016 04:43, Fam Zheng wrote:
> > The batch notification BH needs to know which virtqueues to notify when
> > multiqueue is enabled.  Use a bitmap to track the virtqueues that with
> > pending notifications.
> 
> This approach works great as long as VQs are in the same iothread. An
> alternative way would be using separate BH per VQ, which will naturely work with
> multi queue block layer in the future.  Should we just go for that in the first
> place?  Seems less code churn, and no imaginable disadvantage compared to this
> patch.

It can be slower because all BHs are walked during aio_bh_poll, not just
the scheduled ones.

Paolo