From: Thomas Monjalon <firstname.lastname@example.org> To: Hrvoje Habjanic <email@example.com> Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: [dpdk-ci] [dpdk-users] DPDK TX problems Date: Thu, 26 Mar 2020 21:54:40 +0100 Message-ID: <2735222.2VHbPRQshP@xps> (raw) In-Reply-To: <email@example.com> Thanks for the interesting feedback. It seems we should test this performance use case in our labs. 18/02/2020 09:36, Hrvoje Habjanic: > On 08. 04. 2019. 11:52, Hrvoje Habjanić wrote: > > On 29/03/2019 08:24, Hrvoje Habjanić wrote: > >>> Hi. > >>> > >>> I did write an application using dpdk 17.11 (did try also with 18.11), > >>> and when doing some performance testing, i'm seeing very odd behavior. > >>> To verify that this is not because of my app, i did the same test with > >>> l2fwd example app, and i'm still confused by results. > >>> > >>> In short, i'm trying to push a lot of L2 packets through dpdk engine - > >>> packet processing is minimal. When testing, i'm starting with small > >>> number of packets-per-second, and then gradually increase it to see > >>> where is the limit. At some point, i do reach this limit - packets start > >>> to get dropped. And this is when stuff become weird. > >>> > >>> When i reach peek packet rate (at which packets start to get dropped), i > >>> would expect that reducing packet rate will remove packet drops. But, > >>> this is not the case. For example, let's assume that peek packet rate is > >>> 3.5Mpps. At this point everything works ok. Increasing pps to 4.0Mpps, > >>> makes a lot of dropped packets. When reducing pps back to 3.5Mpps, app > >>> is still broken - packets are still dropped. > >>> > >>> At this point, i need to drastically reduce pps (1.4Mpps) to make > >>> dropped packets go away. Also, app is unable to successfully forward > >>> anything beyond this 1.4M, despite the fact that in the beginning it did > >>> forward 3.5M! Only way to recover is to restart the app. > >>> > >>> Also, sometimes, the app just stops forwarding any packets - packets are > >>> received (as seen by counters), but app is unable to send anything back. > >>> > >>> As i did mention, i'm seeing the same behavior with l2fwd example app. I > >>> did test dpdk 17.11 and also dpdk 18.11 - the results are the same. > >>> > >>> My test environment is HP DL380G8, with 82599ES 10Gig (ixgbe) cards, > >>> connected with Cisco nexus 9300 sw. On the other side is ixia test > >>> appliance. Application is run in virtual machine (VM), using KVM > >>> (openstack, with sriov enabled, and numa restrictions). I did check that > >>> VM is using only cpu's from NUMA node on which network card is > >>> connected, so there is no cross-numa traffic. Openstack is Queens, > >>> Ubuntu is Bionic release. Virtual machine is also using ubuntu bionic > >>> as OS. > >>> > >>> I do not know how to debug this? Does someone else have the same > >>> observations? > >>> > >>> Regards, > >>> > >>> H. > >> There are additional findings. It seems that when i reach peak pps > >> rate, application is not fast enough, and i can see rx missed errors > >> on card statistics on the host. At the same time, tx side starts to > >> show problems (tx burst starts to show it did not send all packets). > >> Shortly after that, tx falls apart completely and top pps rate drops. > >> > >> Since i did not disable pause frames, i can see on the switch "RX > >> pause" frame counter is increasing. On the other hand, if i disable > >> pause frames (on the nic of server), host driver (ixgbe) reports "TX > >> unit hang" in dmesg, and issues card reset. Of course, after reset > >> none of the dpdk apps in VM's on this host does not work. > >> > >> Is it possible that at time of congestion DPDK does not release mbufs > >> back to the pool, and tx ring becomes "filled" with zombie packets > >> (not send by card and also having ref counter as they are in use)? > >> > >> Is there a way to check mempool or tx ring for "left-owers"? Is is > >> possible to somehow "flush" tx ring and/or mempool? > >> > >> H. > > After few more test, things become even weirder - if i do not free mbufs > > which are not sent, but resend them again, i can "survive" over-the-peek > > event! But, then peek rate starts to drop gradually ... > > > > I would ask if someone can try this on their platform and report back? I > > would really like to know if this is problem with my deployment, or > > there is something wrong with dpdk? > > > > Test should be simple - use l2fwd or l3fwd, and determine max pps. Then > > drive pps 30%over max, and then return back and confirm that you can > > still get max pps. > > > > Thanks in advance. > > > > H. > > > > I did receive few mails from users facing this issue, asking how it was > resolved. > > Unfortunately, there is no real fix. It seems that this issue is related > to card and hardware used. I'm still not sure which is more to blame, > but the combination i had is definitely problematic. > > Anyhow, in the end, i did conclude that card driver have some issues > when it is saturated with packets. My suspicion is that driver/software > does not properly free packets, and then DPDK mempool becomes > fragmented, and this causes performance drops. Restarting software > releases pools, and restores proper functionality. > > After no luck with ixgbe, we migrated to Mellanox (4LX), and now there > is no more of this permanent performance drop. With mlx, when limit is > reached, reducing number of packets restores packet forwarding, and this > limit seems to be stable. > > Also, we moved to newer servers - DL380G10, and got significant > performance increase. Also, we moved to newer switch (also cisco), with > 25G ports, which reduced latency - almost by factor of 2! > > I did not try old ixgbe on newer server, but i did try Intel's XL710, > and it is not as happy as Mellanox. It gives better PPS, but it is more > unstable in terms of maximum bw (has similar issues as ixgbe). > > Regards, > > H.
next parent reply index Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <firstname.lastname@example.org> [not found] ` <email@example.com> [not found] ` <firstname.lastname@example.org> 2020-03-26 20:54 ` Thomas Monjalon [this message] 2020-03-27 18:25 ` Lincoln Lavoie
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