linux-kernel - Re: [PATCH 5/5] virtio-scsi: introduce multiqueue support

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Message-ID: <20120904124800.GE9805@redhat.com>
Date:	Tue, 4 Sep 2012 15:48:00 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	kvm@...r.kernel.org, rusty@...tcorp.com.au, jasowang@...hat.com,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 5/5] virtio-scsi: introduce multiqueue support

On Tue, Aug 28, 2012 at 01:54:17PM +0200, Paolo Bonzini wrote:
> This patch adds queue steering to virtio-scsi.  When a target is sent
> multiple requests, we always drive them to the same queue so that FIFO
> processing order is kept.  However, if a target was idle, we can choose
> a queue arbitrarily.  In this case the queue is chosen according to the
> current VCPU, so the driver expects the number of request queues to be
> equal to the number of VCPUs.  This makes it easy and fast to select
> the queue, and also lets the driver optimize the IRQ affinity for the
> virtqueues (each virtqueue's affinity is set to the CPU that "owns"
> the queue).
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

I guess an alternative is a per-target vq.
Is the reason you avoid this that you expect more targets
than cpus? If yes this is something you might want to
mention in the log.
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