On Tue, Nov 28, 2017 at 09:36:37AM +0800, Jason Wang wrote: > > > On 2017年11月28日 00:21, Wei Xu wrote: > > On Mon, Nov 20, 2017 at 02:25:17PM -0500, Matthew Rosato wrote: > > > On 11/14/2017 03:11 PM, Matthew Rosato wrote: > > > > On 11/12/2017 01:34 PM, Wei Xu wrote: > > > > > On Sat, Nov 11, 2017 at 03:59:54PM -0500, Matthew Rosato wrote: > > > > > > > > This case should be quite similar with pkgten, if you got > > > > > > > > improvement with > > > > > > > > pktgen, usually it was also the same for UDP, could you please > > > > > > > > try to disable > > > > > > > > tso, gso, gro, ufo on all host tap devices and guest virtio-net > > > > > > > > devices? Currently > > > > > > > > the most significant tests would be like this AFAICT: > > > > > > > > > > > > > > > > Host->VM 4.12 4.13 > > > > > > > > TCP: > > > > > > > > UDP: > > > > > > > > pktgen: > > > So, I automated these scenarios for extended overnight runs and started > > > experiencing OOM conditions overnight on a 40G system. I did a bisect > > > and it also points to c67df11f. I can see a leak in at least all of the > > > Host->VM testcases (TCP, UDP, pktgen), but the pktgen scenario shows the > > > fastest leak. > > > > > > I enabled slub_debug on base 4.13 and ran my pktgen scenario in short > > > intervals until a large% of host memory was consumed. Numbers below > > > after the last pktgen run completed. The summary is that a very large # > > > of active skbuff_head_cache entries can be seen - The sum of alloc/free > > > calls match up, but the # of active skbuff_head_cache entries keeps > > > growing each time the workload is run and never goes back down in > > > between runs. > > > > > > free -h: > > > total used free shared buff/cache available > > > Mem: 39G 31G 6.6G 472K 1.4G 6.8G > > > > > > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > > > > > 1001952 1000610 99% 0.75K 23856 42 763392K > > > skbuff_head_cache > > > 126192 126153 99% 0.36K 2868 44 45888K ksm_rmap_item > > > 100485 100435 99% 0.41K 1305 77 41760K kernfs_node_cache > > > 63294 39598 62% 0.48K 959 66 30688K dentry > > > 31968 31719 99% 0.88K 888 36 28416K inode_cache > > > > > > /sys/kernel/slab/skbuff_head_cache/alloc_calls : > > > 259 __alloc_skb+0x68/0x188 age=1/135076/135741 pid=0-11776 > > > cpus=0,2,4,18 > > > 1000351 __build_skb+0x42/0xb0 age=8114/63172/117830 pid=0-11863 cpus=0,10 > > > > > > /sys/kernel/slab/skbuff_head_cache/free_calls: > > > 13492 <not-available> age=4295073614 pid=0 cpus=0 > > > 978298 tun_do_read.part.10+0x18c/0x6a0 age=8532/63624/110571 pid=11733 > > > cpus=1-19 > > > 6 skb_free_datagram+0x32/0x78 age=11648/73253/110173 pid=11325 > > > cpus=4,8,10,12,14 > > > 3 __dev_kfree_skb_any+0x5e/0x70 age=108957/115043/118269 > > > pid=0-11605 cpus=5,7,12 > > > 1 netlink_broadcast_filtered+0x172/0x470 age=136165 pid=1 cpus=4 > > > 2 netlink_dump+0x268/0x2a8 age=73236/86857/100479 pid=11325 > > > cpus=4,12 > > > 1 netlink_unicast+0x1ae/0x220 age=12991 pid=9922 cpus=12 > > > 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11776 cpus=6 > > > 3 unix_stream_read_generic+0x810/0x908 age=15443/50904/118273 > > > pid=9915-11581 cpus=8,16,18 > > > 2 tap_do_read+0x16a/0x488 [tap] age=42338/74246/106155 > > > pid=11605-11699 cpus=2,9 > > > 1 macvlan_process_broadcast+0x17e/0x1e0 [macvlan] age=18835 > > > pid=331 cpus=11 > > > 8800 pktgen_thread_worker+0x80a/0x16d8 [pktgen] age=8545/62184/110571 > > > pid=11863 cpus=0 > > > > > > > > > By comparison, when running 4.13 with c67df11f reverted, here's the same > > > output after the exact same test: > > > > > > free -h: > > > total used free shared buff/cache available > > > Mem: 39G 783M 37G 472K 637M 37G > > > > > > slabtop: > > > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > > 714 256 35% 0.75K 17 42 544K skbuff_head_cache > > > > > > /sys/kernel/slab/skbuff_head_cache/alloc_calls: > > > 257 __alloc_skb+0x68/0x188 age=0/65252/65507 pid=1-11768 cpus=10,15 > > > /sys/kernel/slab/skbuff_head_cache/free_calls: > > > 255 <not-available> age=4295003081 pid=0 cpus=0 > > > 1 netlink_broadcast_filtered+0x2e8/0x4e0 age=65601 pid=1 cpus=15 > > > 1 tcp_recvmsg+0x2e2/0xa60 age=0 pid=11768 cpus=16 > > > > > Thanks a lot for the test, and sorry for the late update, I was working on > > the code path and didn't find anything helpful to you till today. > > > > I did some tests and initially it turned out that the bottleneck was the > > guest > > kernel stack(napi) side, followed by tracking the traffic footprints and it > > appeared as the loss happened when vring was full and could not be drained > > out by the guest, afterwards it triggered a SKB drop in vhost driver due > > to no headcount to fill it with, it can be avoided by deferring consuming > > the > > SKB after having obtained a sufficient headcount with below patch. > > > > Could you please try it? It is based on 4.13 and I also applied Jason's > > 'conditionally enable tx polling' patch. > > https://lkml.org/lkml/2016/6/1/39 > > This patch has already been merged. > > > > > I only tested one instance case from Host -> VM with uperf & iperf3, I like > > iperf3 a bit more since it spontaneously tells the retransmitted and cwnd > > during testing. :) > > > > To maximize the performance of one instance case, two vcpus are needed, > > one does the kernel napi and the other one should serve the socket syscall > > (mostly reading) from uperf/iperf userspace, so I set two vcpus to the guest > > and pinned the iperf/uperf slave to the one not used by kernel napi, you may > > need to check out which one you should pin properly by seeing the CPU > > utilization with a quick trial test before running the long duration test. > > > > Slight performance improvement for tcp with the patch(host/guest offload > > off) > > on x86, also 4.12 wins the game with 20-30% possibility from time to time, > > but > > the cwnd and retransmitted statistics are almost the same now, the 'retrans' > > was about 10x times more and cwnd was 6x smaller than 4.12 before. > > > > Here is one typical sample of my tests. > > 4.12 4.13 > > offload on: 36.8Gbits 37.4Gbits > > offload off: 7.68Gbits 7.84Gbits > > > > I also borrowed a s390x machine with 6 cpus and 4G memory from system z > > team, > > it seems 4.12 is still a bit faster than 4.13, could you please see if this > > is aligned with your test bed? > > 4.12 4.13 > > offload on: 37.3Gbits 38.3Gbits > > offload off: 6.26Gbits 6.06Gbits > > > > For pktgen, I got 10% improvement(xdp1 drop on guest) which is a bit faster > > than Jason's number before. > > 4.12 4.13 > > 3.33 Mpss 3.70 Mpps > > > > Thanks again for all the tests your have done. > > > > Wei > > > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -776,8 +776,6 @@ static void handle_rx(struct vhost_net *net) > > /* On error, stop handling until the next kick. */ > > if (unlikely(headcount < 0)) > > goto out; > > - if (nvq->rx_array) > > - msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > > /* On overrun, truncate and discard */ > > if (unlikely(headcount > UIO_MAXIOV)) { > > I think you need do msg.msg_control = vhost_net_buf_consume() here too. > > > iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > > @@ -798,6 +796,10 @@ static void handle_rx(struct vhost_net *net) > > * they refilled. */ > > goto out; > > } > > + > > + if (nvq->rx_array) > > + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > > + > > /* We don't need to be notified again. */ > > iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len); > > fixup = msg.msg_iter; > > > > > > Good catch, this fixes the memory leak too. > > I suggest to post a formal patch for -net as soon as possible too since it > was a valid fix even if it does not help for performance.
OK, will post it soon. Wei > > Thanks
