On 08/25/2013 07:53 PM, Michael S. Tsirkin wrote: > 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? The result is, I see about 5%-10% improvement for per cpu throughput on guest tx. But about 5% degradation on per cpu transaction rate on TCP_RR. >> 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? > 5%-10% improvement on for per cpu throughput on guest rx, but some regressions (5%) on guest tx. So we'd better keep and make it doing properly. Will post V2 for your reviewing. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
