Date: Mon, 9 Jun 2014 17:02:46 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: current@FreeBSD.org, net@FreeBSD.org Subject: dhclient sucks cpu usage... Message-ID: <20140610000246.GW31367@funkthat.com>
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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... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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