Date: Fri, 27 Oct 2006 18:25:05 -0700 From: Julian Elischer <julian@elischer.org> To: "Alexandre \"Sunny\" Kovalenko" <Alex.Kovalenko@verizon.net> Cc: Daniel Eischen <deischen@freebsd.org>, Paul Allen <nospam@ugcs.caltech.edu>, current@freebsd.org Subject: Re: Comments on the KSE option Message-ID: <4542B171.8050601@elischer.org> In-Reply-To: <1161998104.872.18.camel@RabbitsDen.RabbitsLawn.verizon.net> References: <45425D92.8060205@elischer.org> <20061027201838.GH30707@riyal.ugcs.caltech.edu> <Pine.GSO.4.64.0610271634160.7105@sea.ntplx.net> <1161998104.872.18.camel@RabbitsDen.RabbitsLawn.verizon.net>
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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 <julian@elischer.org>, 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.)
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