From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Xu Subject: Re: Regression in throughput between kvm guests over virtual bridge Date: Wed, 29 Nov 2017 02:00:47 +0800 Message-ID: <20171128180047.5tojixyh4zagened@Wei-Dev> References: <56710dc8-f289-0211-db97-1a1ea29e38f7@linux.vnet.ibm.com> <20171104233519.7jwja7t2itooyeak@Wei-Dev> <1611b26f-0997-3b22-95f5-debf57b7be8c@linux.vnet.ibm.com> <101d1fdf-9df1-44bd-73a7-e7d8fbc09160@linux.vnet.ibm.com> <20171112183406.zuuj7w3fmtb4eduf@Wei-Dev> <9996b0f1-ffa6-ff95-2e9c-0deccf4623ae@linux.vnet.ibm.com> <20171127162109.eriexz7gpvz6vxnx@Wei-Dev> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Jason Wang , mst@redhat.com, netdev@vger.kernel.org, davem@davemloft.net To: Matthew Rosato Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46874 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752625AbdK1RjU (ORCPT ); Tue, 28 Nov 2017 12:39:20 -0500 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Nov 27, 2017 at 09:44:07PM -0500, Matthew Rosato wrote: > On 11/27/2017 08:36 PM, 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 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 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. > >> Thanks > > > > +1 to posting this patch formally. I also verified that it resolves the > memory leak I was experiencing. > > In terms of performance numbers, here are quick #s using the original > environment where the regression was noted (4GB, 4vcpu guests, no CPU > binding, TCP VM<->VM): > > 4.12: 34.71Gb/s > 4.13: 18.80Gb/s > 4.13+: 38.26Gb/s > Great to know the number, patch sent, thanks you so much for all your profound tests, it really helped a lot to figure it out. Wei > I'll keep running numbers, but that looks very promising. >