From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-scsi@vger.kernel.org,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 5/5] virtio-scsi: introduce multiqueue support
Date: Tue, 4 Sep 2012 17:21:54 +0300 [thread overview]
Message-ID: <20120904142154.GL9805@redhat.com> (raw)
In-Reply-To: <504606F6.4080603@redhat.com>
On Tue, Sep 04, 2012 at 03:49:42PM +0200, Paolo Bonzini wrote:
> Il 04/09/2012 14:48, Michael S. Tsirkin ha scritto:
> >> > 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@redhat.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.
>
> One reason is that, even though in practice I expect roughly the same
> number of targets and VCPUs, hotplug means the number of targets is
> difficult to predict and is usually fixed to 256.
>
> The other reason is that per-target vq didn't give any performance
> advantage. The bonus comes from cache locality and less process
> migrations, more than from the independent virtqueues.
>
> Paolo
Okay, and why is per-target worse for cache locality?
--
MST
next prev parent reply other threads:[~2012-09-04 14:21 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-28 11:54 [PATCH 0/5] Multiqueue virtio-scsi Paolo Bonzini
2012-08-28 11:54 ` [PATCH 1/5] virtio-ring: move queue_index to vring_virtqueue Paolo Bonzini
2012-08-29 7:54 ` Jason Wang
2012-09-05 23:32 ` Rusty Russell
2012-08-28 11:54 ` [PATCH 2/5] virtio: introduce an API to set affinity for a virtqueue Paolo Bonzini
2012-09-05 23:32 ` Rusty Russell
2012-08-28 11:54 ` [PATCH 3/5] virtio-scsi: allocate target pointers in a separate memory block Paolo Bonzini
2012-08-28 14:07 ` Sasha Levin
2012-08-28 14:25 ` Paolo Bonzini
2012-08-28 11:54 ` [PATCH 4/5] virtio-scsi: pass struct virtio_scsi to virtqueue completion function Paolo Bonzini
2012-08-28 11:54 ` [PATCH 5/5] virtio-scsi: introduce multiqueue support Paolo Bonzini
2012-09-04 2:21 ` Nicholas A. Bellinger
2012-09-04 6:46 ` Paolo Bonzini
2012-09-04 8:46 ` Michael S. Tsirkin
2012-09-04 10:25 ` Paolo Bonzini
2012-09-04 11:09 ` Michael S. Tsirkin
2012-09-04 11:18 ` Paolo Bonzini
2012-09-04 13:35 ` Michael S. Tsirkin
2012-09-04 13:45 ` Paolo Bonzini
2012-09-04 14:19 ` Michael S. Tsirkin
2012-09-04 14:25 ` Paolo Bonzini
2012-09-04 20:11 ` Nicholas A. Bellinger
2012-09-05 7:03 ` Paolo Bonzini
2012-09-04 12:48 ` Michael S. Tsirkin
2012-09-04 13:49 ` Paolo Bonzini
2012-09-04 14:21 ` Michael S. Tsirkin [this message]
2012-09-04 14:30 ` Paolo Bonzini
2012-09-04 14:41 ` Michael S. Tsirkin
2012-09-04 14:47 ` Michael S. Tsirkin
2012-09-04 14:55 ` Paolo Bonzini
2012-09-04 15:03 ` Michael S. Tsirkin
2012-08-30 7:13 ` [PATCH 0/5] Multiqueue virtio-scsi Stefan Hajnoczi
2012-08-30 14:53 ` Michael S. Tsirkin
2012-08-30 15:45 ` Paolo Bonzini
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