[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] value of VIRTQUEUE_MAX_SIZE

From: Peter Lieven
Subject: Re: [Qemu-devel] value of VIRTQUEUE_MAX_SIZE
Date: Thu, 05 Feb 2015 15:29:17 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

Am 05.02.2015 um 15:00 schrieb Stefan Hajnoczi:
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

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

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?

The idea was that IOV_MAX is the limit in case of at least virtio-blk. The host
will not support more than IOV_MAX iovecs passed to a block request.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]