From owner-freebsd-current@FreeBSD.ORG Tue Jun 10 00:02:54 2014 Return-Path: Delivered-To: current@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 750183F6; Tue, 10 Jun 2014 00:02:54 +0000 (UTC) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "funkthat.com", Issuer "funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 52A3C20EA; Tue, 10 Jun 2014 00:02:53 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id s5A02kIq066075 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 9 Jun 2014 17:02:46 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id s5A02kjk066074; Mon, 9 Jun 2014 17:02:46 -0700 (PDT) (envelope-from jmg) Date: Mon, 9 Jun 2014 17:02:46 -0700 From: John-Mark Gurney To: current@FreeBSD.org, net@FreeBSD.org Subject: dhclient sucks cpu usage... Message-ID: <20140610000246.GW31367@funkthat.com> Mail-Followup-To: current@FreeBSD.org, net@FreeBSD.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Mon, 09 Jun 2014 17:02:46 -0700 (PDT) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 10 Jun 2014 00:02:54 -0000 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."