From owner-freebsd-arch@FreeBSD.ORG Wed Feb 19 23:07:21 2014 Return-Path: Delivered-To: freebsd-arch@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 A26CCD34; Wed, 19 Feb 2014 23:07:21 +0000 (UTC) Received: from zxy.spb.ru (zxy.spb.ru [195.70.199.98]) by mx1.freebsd.org (Postfix) with ESMTP id 4D1621E1E; Wed, 19 Feb 2014 23:07:21 +0000 (UTC) Received: from slw by zxy.spb.ru with local (Exim 4.69 (FreeBSD)) (envelope-from ) id 1WGGEZ-000Fl4-Uw; Thu, 20 Feb 2014 03:07:19 +0400 Date: Thu, 20 Feb 2014 03:07:19 +0400 From: Slawa Olhovchenkov To: Alexander Motin Subject: Re: [rfc] bind per-cpu timeout threads to each CPU Message-ID: <20140219230719.GM83358@zxy.spb.ru> References: <530508B7.7060102@FreeBSD.org> <53050D24.3020505@FreeBSD.org> <53051C71.3050705@FreeBSD.org> <20140219214428.GA53864@zxy.spb.ru> <53052B80.3010505@FreeBSD.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53052B80.3010505@FreeBSD.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: slw@zxy.spb.ru X-SA-Exim-Scanned: No (on zxy.spb.ru); SAEximRunCond expanded to false Cc: Adrian Chadd , freebsd-current , Jeffrey Faden , "freebsd-arch@freebsd.org" X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Feb 2014 23:07:21 -0000 On Thu, Feb 20, 2014 at 12:09:04AM +0200, Alexander Motin wrote: > On 19.02.2014 23:44, Slawa Olhovchenkov wrote: > > On Wed, Feb 19, 2014 at 11:04:49PM +0200, Alexander Motin wrote: > > > >> On 19.02.2014 22:04, Adrian Chadd wrote: > >>> On 19 February 2014 11:59, Alexander Motin wrote: > >>> > >>>>> So if we're moving towards supporting (among others) a pcbgroup / RSS > >>>>> hash style work load distribution across CPUs to minimise > >>>>> per-connection lock contention, we really don't want the scheduler to > >>>>> decide it can schedule things on other CPUs under enough pressure. > >>>>> That'll just make things worse. > >>> > >>>> True, though it is also not obvious that putting second thread on CPU run > >>>> queue is better then executing it right now on another core. > >>> > >>> Well, it depends if you're trying to optimise for "run all runnable > >>> tasks as quickly as possible" or "run all runnable tasks in contexts > >>> that minimise lock contention." > >>> > >>> The former sounds great as long as there's no real lock contention > >>> going on. But as you add more chances for contention (something like > >>> "100,000 concurrent TCP flows") then you may end up having your TCP > >>> timer firing stuff interfere with more TXing or RXing on the same > >>> connection. > >> > >> 100K TCP flows probably means 100K locks. That means that chance of lock > >> collision on each of them is effectively zero. More realistic it could > > > > What about 100K/N_cpu*PPS timer's queue locks for remove/insert TCP > > timeouts callbacks? > > I am not sure what this formula means, but yes, per-CPU callout locks > can much more likely be congested. They are only per-CPU, not per-flow. 100K TCP flows distributed between CPU (100K/N_cpu). every TCP flow several times per seconds touch his callout (*PPS)