|
From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] Re: [PATCH 2/3] virtio network device |
Date: | Tue, 11 Dec 2007 19:40:43 -0600 |
User-agent: | Thunderbird 2.0.0.6 (X11/20071022) |
Rusty Russell wrote:
On Sunday 09 December 2007 09:02:48 Anthony Liguori wrote:If QEMU ever got true SMP support, then virtio would not work as it requires 16-bit atomic writes which AFAIK is not possible on a number of non-x86 architectures.Hmm? Where is this requirement coming from?I think everyone should stop using the word "atomic" in virtio discussions; it's confusing.
The virtio ring queue indices are 16-bit and are readable to one end while writable on the other end. To ensure that this can be done in a lock-less way, it's necessary to atomically update the index. Atomic is the right word here because if the 16-bit write gets converted into two 8-bit writes, then very bad things could happen with SMP.
Regards, Anthony Liguori
Rusty.
[Prev in Thread] | Current Thread | [Next in Thread] |