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.




Reply via email to