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 <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. > >> 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. >
