Date: Tue, 10 Jun 2014 13:11:36 -0500 (CDT) From: Bryan Venteicher <bryanv@daemoninthecloset.org> To: "Alexander V. Chernikov" <melifaro@FreeBSD.org> Cc: John-Mark Gurney <jmg@funkthat.com>, current@FreeBSD.org, net@FreeBSD.org Subject: Re: dhclient sucks cpu usage... Message-ID: <1520746932.4518.1402423896830.JavaMail.root@daemoninthecloset.org> In-Reply-To: <5396CD41.2080300@FreeBSD.org> References: <20140610000246.GW31367@funkthat.com> <100488220.4292.1402369436876.JavaMail.root@daemoninthecloset.org> <5396CD41.2080300@FreeBSD.org>
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----- 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(): 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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