On Fri, Aug 23, 2013 at 04:55:49PM +0800, Jason Wang wrote: > On 08/20/2013 10:48 AM, Jason Wang wrote: > > On 08/16/2013 06:02 PM, Michael S. Tsirkin wrote: > >> > On Fri, Aug 16, 2013 at 01:16:30PM +0800, Jason Wang wrote: > >>> >> We used to limit the max pending DMAs to prevent guest from pinning too many > >>> >> pages. But this could be removed since: > >>> >> > >>> >> - We have the sk_wmem_alloc check in both tun/macvtap to do the same work > >>> >> - This max pending check were almost useless since it was one done when there's > >>> >> no new buffers coming from guest. Guest can easily exceeds the limitation. > >>> >> - We've already check upend_idx != done_idx and switch to non zerocopy then. So > >>> >> even if all vq->heads were used, we can still does the packet transmission. > >> > We can but performance will suffer. > > The check were in fact only done when no new buffers submitted from > > guest. So if guest keep sending, the check won't be done. > > > > If we really want to do this, we should do it unconditionally. Anyway, I > > will do test to see the result. > > There's a bug in PATCH 5/6, the check: > > nvq->upend_idx != nvq->done_idx > > makes the zerocopy always been disabled since we initialize both > upend_idx and done_idx to zero. So I change it to: > > (nvq->upend_idx + 1) % UIO_MAXIOV != nvq->done_idx. But what I would really like to try is limit ubuf_info to VHOST_MAX_PEND. I think this has a chance to improve performance since we'll be using less cache. Of course this means we must fix the code to really never submit more than VHOST_MAX_PEND requests. Want to try? > > With this change on top, I didn't see performance difference w/ and w/o > this patch. Did you try small message sizes btw (like 1K)? Or just netperf default of 64K? -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
