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 I'll keep running numbers, but that looks very promising.
