From owner-freebsd-current@FreeBSD.ORG Sat Oct 28 03:51:06 2006 Return-Path: X-Original-To: current@freebsd.org Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 6E45A16A40F; Sat, 28 Oct 2006 03:51:06 +0000 (UTC) (envelope-from prvs=julian=449da6880@elischer.org) Received: from a50.ironport.com (a50.ironport.com [63.251.108.112]) by mx1.FreeBSD.org (Postfix) with ESMTP id 2E0DF43D45; Sat, 28 Oct 2006 03:51:06 +0000 (GMT) (envelope-from prvs=julian=449da6880@elischer.org) Received: from unknown (HELO [192.168.2.4]) ([10.251.60.61]) by a50.ironport.com with ESMTP; 27 Oct 2006 20:51:04 -0700 Message-ID: <4542D3A8.1040500@elischer.org> Date: Fri, 27 Oct 2006 20:51:04 -0700 From: Julian Elischer User-Agent: Thunderbird 1.5.0.7 (Macintosh/20060909) MIME-Version: 1.0 To: "Alexandre \"Sunny\" Kovalenko" References: <45425D92.8060205@elischer.org> <20061027201838.GH30707@riyal.ugcs.caltech.edu> <1161998104.872.18.camel@RabbitsDen.RabbitsLawn.verizon.net> <4542B171.8050601@elischer.org> <1161999387.872.29.camel@RabbitsDen.RabbitsLawn.verizon.net> In-Reply-To: <1161999387.872.29.camel@RabbitsDen.RabbitsLawn.verizon.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Daniel Eischen , Paul Allen , current@freebsd.org Subject: Re: Comments on the KSE option X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 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: Sat, 28 Oct 2006 03:51:06 -0000 Alexandre "Sunny" Kovalenko wrote: > On Fri, 2006-10-27 at 18:25 -0700, Julian Elischer wrote: >> Alexandre "Sunny" Kovalenko wrote: >>> On Fri, 2006-10-27 at 16:41 -0400, Daniel Eischen wrote: >>>> On Fri, 27 Oct 2006, Paul Allen wrote: >>>> >>>>>> From Julian Elischer , Fri, Oct 27, 2006 at 12:27:14PM -0700: >>>>>> The aim of the fair scheduling code is to ensure that if you, as a user, >>>>>> make a process that starts 1000 threads, and I as a user, make an >>>>>> unthreaded process, then I can still get to the CPU at somewhat similar >>>>>> rates to you. A naive scheduler would give you 1000 cpu slots and me 1. >>>>> Ah. Let me be one of the first to take a crack at attacking this idea as >>>>> a mistake. >>>> No, it is POSIX. You, the application, can write a program with >>>> system scope or process scope threads and get whatever you behavior >>>> you want, within rlimits of course. >>>> >>>> If you want unfair scheduling, then create your threads with >>>> system scope contention, otherwise use process scope. The >>>> kernel should be designed to allow both, and have adjustable >>>> limits in place for (at least) system scope threads. >>>> >>>> Noone is saying that you can't have as many system scope threads >>>> as you want (and as allowed by limits), just that you must also >>>> be able to have process scope threads (with probably higher limits >>>> or possibly no limits). >>>> >>> I might be missing something here, but OP was separating M:N (which is >>> what you are referring to above), and "fairness" (not giving process >>> with 1000 *system scope* threads 1000 CPU scheduling slots). As far as I >>> know the first one is POSIX and the second one is not. >>> >>> FWIW: as an application programmer who spent considerable amount of time >>> lately trying to make heavily multithreaded application run most >>> efficiently on 32-way machine, I would rather not have to deal with >>> "fairness" -- M:N is bad enough. >>> >> >> no, fairness is making sure that 1000 process scope threads >> do not negatively impact other processes. >> 1000 system scope threads are controlled by your ulimit settings >> (Each one counts as a process.) >> >> > I apologize for misinterpreting your words. But then, if I have M:N set > to 10:1, I would expect application with 1000 process scope threads to > have as many CPU slots as 100 processes, or, if I have 10 system scope > threads and 990 process scope threads, I would expect application to > have as many CPU slots as 109 processes. Is this what you refer to as > "fairness"? > M:N is not a ratio, but rather the notation to say that M user threads are enacted using N kernel schedulable entities (kernel threads). usually N is limited to something like NCPU kernel schedulable entities running at a time. (not including sleeping threads waiting for IO) (NCPU is the number of CPUs). so in fact M:N is usually M user threads over over some number like 4 or 8 kernel threads (depending on #cpus) plus the number of threads waiting for IO. Julian