From: Stefan Hajnoczi <stefanha@gmail.com>
To: Peter Lieven <pl@kamp.de>
Cc: Kevin Wolf <kwolf@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
ming.lei@canonical.com,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
Max Reitz <mreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] value of VIRTQUEUE_MAX_SIZE
Date: Thu, 5 Feb 2015 14:00:29 +0000 [thread overview]
Message-ID: <20150205140029.GF19277@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <54CBF2B2.20703@kamp.de>
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On Fri, Jan 30, 2015 at 10:08:02PM +0100, Peter Lieven wrote:
> Just wondering if VIRTQUEUE_MAX_SIZE in include/hw/virtio/virtio.h should not be equal to IOV_MAX instead of the hardcoded 1024?
The vring queue size is guest-visible to some extent (e.g. vring memory
layout). Tying it to a constant that is defined by the host operating
system could lead to problems (e.g. live migration between different
hosts).
Anyway, all of the virtio devices have a queue size that is less than or
equal to VIRTQUEUE_MAX_SIZE (and there is an assertion to check this in
virtio_add_queue()).
Guests are supposed to honor the vring queue size, although indirect
descriptors seem to be able to use up to VIRTQUEUE_MAX_SIZE according to
my understanding of QEMU's virtio.c code.
Why would you like to use IOV_MAX?
Stefan
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next prev parent reply other threads:[~2015-02-05 14:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-30 21:08 [Qemu-devel] value of VIRTQUEUE_MAX_SIZE Peter Lieven
2015-02-05 14:00 ` Stefan Hajnoczi [this message]
2015-02-05 14:29 ` Peter Lieven
2015-02-06 10:42 ` Stefan Hajnoczi
2015-02-06 10:45 ` Peter Lieven
2015-02-06 13:22 ` Eric Blake
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