On Wed, 2010-09-29 at 10:28 +0200, Michael S. Tsirkin wrote: > > > 1. Adding completion field in struct virtqueue; > > > 2. when it is a zero copy packet, put vhost thread wait for > completion > > > to update vhost_add_used_and_signal; > > > 3. passing vq from vhost to macvtap as skb destruct_arg; > > > 4. when skb is freed for the last reference, signal vq completion > > > The test results show same performance as the original patch. How > do you > > > think? If it sounds good to you. I will resubmit this reversion > patch. > > > The patch still keeps as simple as it was before. :) > > > > > > Thanks > > > Shirley > > > > If you look at dev_hard_start_xmit you will see a call > > to skb_orphan_try which often calls the skb destructor. > > So I suspect this is almost equivalent to your original patch, > > and has the same correctness issue. > > So you could try doing skb_tx(skb)->prevent_sk_orphan = 1 > just to see what will happen. Might be interesting - just > make sure the device doesn't orphan the skb first thing. > I suspect lack of parallelism will result in bad throughput > esp for small messages. > > Note this still won't make it correct (this has module unloading > issue, and devices might still orphan skb, clone it, or hang on to > paged data in some other way) but at least closer. For message size smaller than 128, it still does copy. I tested some small message size, I didn't see any regression. I will run more test to focus on small message size between 128 - 4K. I don't need prevent_sk_orphan since in skb_release_data for last reference, I just need the ZEROCOPY flag from that sock to signal a completion. Thanks Shirley -- 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
