Date: Tue, 10 Jun 2014 22:21:23 +0400 From: "Alexander V. Chernikov" <melifaro@FreeBSD.org> To: Bryan Venteicher <bryanv@daemoninthecloset.org> Cc: John-Mark Gurney <jmg@funkthat.com>, current@FreeBSD.org, net@FreeBSD.org Subject: Re: dhclient sucks cpu usage... Message-ID: <53974CA3.7010701@FreeBSD.org> In-Reply-To: <1520746932.4518.1402423896830.JavaMail.root@daemoninthecloset.org> References: <20140610000246.GW31367@funkthat.com> <100488220.4292.1402369436876.JavaMail.root@daemoninthecloset.org> <5396CD41.2080300@FreeBSD.org> <1520746932.4518.1402423896830.JavaMail.root@daemoninthecloset.org>
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On 10.06.2014 22:11, Bryan Venteicher wrote: > > ----- Original Message ----- >> On 10.06.2014 07:03, Bryan Venteicher wrote: >>> Hi, >>> >>> ----- Original Message ----- >>>> So, after finding out that nc has a stupidly small buffer size (2k >>>> even though there is space for 16k), I was still not getting as good >>>> as performance using nc between machines, so I decided to generate some >>>> flame graphs to try to identify issues... (Thanks to who included a >>>> full set of modules, including dtraceall on memstick!) >>>> >>>> So, the first one is: >>>> https://www.funkthat.com/~jmg/em.stack.svg >>>> >>>> As I was browsing around, the em_handle_que was consuming quite a bit >>>> of cpu usage for only doing ~50MB/sec over gige.. Running top -SH shows >>>> me that the taskqueue for em was consuming about 50% cpu... Also pretty >>>> high for only 50MB/sec... Looking closer, you'll see that bpf_mtap is >>>> consuming ~3.18% (under ether_nh_input).. I know I'm not running tcpdump >>>> or anything, but I think dhclient uses bpf to be able to inject packets >>>> and listen in on them, so I kill off dhclient, and instantly, the >>>> taskqueue >>>> thread for em drops down to 40% CPU... (transfer rate only marginally >>>> improves, if it does) >>>> >>>> I decide to run another flame graph w/o dhclient running: >>>> https://www.funkthat.com/~jmg/em.stack.nodhclient.svg >>>> >>>> and now _rxeof drops from 17.22% to 11.94%, pretty significant... >>>> >>>> So, if you care about performance, don't run dhclient... >>>> >>> Yes, I've noticed the same issue. It can absolutely kill performance >>> in a VM guest. It is much more pronounced on only some of my systems, >>> and I hadn't tracked it down yet. I wonder if this is fallout from >>> the callout work, or if there was some bpf change. >>> >>> I've been using the kludgey workaround patch below. >> Hm, pretty interesting. >> dhclient should setup proper filter (and it looks like it does so: >> 13:10 [0] m@ptichko s netstat -B >> Pid Netif Flags Recv Drop Match Sblen Hblen Command >> 1224 em0 -ifs--l 41225922 0 11 0 0 dhclient >> ) >> see "match" count. >> And BPF itself adds the cost of read rwlock (+ bgp_filter() calls for >> each consumer on interface). >> It should not introduce significant performance penalties. >> > > It will be a bit before I'm able to capture that. Here's a Flamegraph from > earlier in the year showing an absurd amount of time spent in bpf_mtap(): Can you briefly describe test setup? (Actually I'm interested in overall pps rate, bpf filter used and match ratio). For example, for some random box at $work: 22:17 [0] m@sas1-fw1 netstat -I vlan802 -w1 input (vlan802) output packets errs idrops bytes packets errs bytes colls 430418 0 0 337712454 396282 0 333207773 0 CPU: 0.4% user, 0.0% nice, 1.2% system, 15.9% interrupt, 82.5% idle 2:17 [0] sas1-fw1# tcpdump -i vlan802 -lnps0 icmp and host X.X.X.X tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vlan802, link-type EN10MB (Ethernet), capture size 65535 bytes 22:17:14.866085 IP X.X.X.X > Y.Y.Y.Y: ICMP echo request, id 6730, seq 1, length 64 22:17 [0] m@sas1-fw1 s netstat -B 2>/dev/null | grep tcpdump 98520 vlan802 ---s--- 27979422 0 40 0 0 tcpdump CPU: 0.9% user, 0.0% nice, 2.7% system, 17.6% interrupt, 78.8% idle (Actually the load is floating due to bursty traffic in 14-20% rate but I can't see much difference with tcpdump turned on/off). > > http://people.freebsd.org/~bryanv/vtnet/vtnet-bpf-10.svg > > >>> diff --git a/sys/net/bpf.c b/sys/net/bpf.c >>> index cb3ed27..9751986 100644 >>> --- a/sys/net/bpf.c >>> +++ b/sys/net/bpf.c >>> @@ -2013,9 +2013,11 @@ bpf_gettime(struct bintime *bt, int tstype, struct >>> mbuf *m) >>> return (BPF_TSTAMP_EXTERN); >>> } >>> } >>> +#if 0 >>> if (quality == BPF_TSTAMP_NORMAL) >>> binuptime(bt); >>> else >>> +#endif >> bpf_getttime() is called IFF packet filter matches some traffic. >> Can you show your "netstat -B" output ? >>> getbinuptime(bt); >>> >>> return (quality); >>> >>> >>>> -- >>>> John-Mark Gurney Voice: +1 415 225 5579 >>>> >>>> "All that I will do, has been done, All that I have, has not." >>>> _______________________________________________ >>>> freebsd-current@freebsd.org mailing list >>>> http://lists.freebsd.org/mailman/listinfo/freebsd-current >>>> To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" >>>> >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> http://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >>> >>
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