Date: Sun, 29 Oct 2006 09:24:07 -0700 From: Scott Long <scottl@samsco.org> To: Robert Watson <rwatson@freebsd.org> Cc: Lucas James <Lucas.James@ldjcs.com.au>, freebsd-current@freebsd.org Subject: Re: Comments on the KSE option Message-ID: <4544D5A7.8070604@samsco.org> In-Reply-To: <20061029090945.P27107@fledge.watson.org> References: <45425D92.8060205@elischer.org> <20061028194125.GL30707@riyal.ugcs.caltech.edu> <Pine.GSO.4.64.0610282106500.14917@sea.ntplx.net> <200610291257.11744.Lucas.James@ldjcs.com.au> <20061029090945.P27107@fledge.watson.org>
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Robert Watson wrote: > > On Sun, 29 Oct 2006, Lucas James wrote: > >> I read what Paul said was that system scope threads have a different >> "fairness" than processes. ie: >> >> If your application requires 1000 threads of execution, you can write >> it three ways, with 1000 processes, 1000 system scope threads or 1000 >> process scope threads (or a mix of the three). >> >> This whole "fairness" argument is about making system scope threads >> have the same priority as process scope threads. It leaves out the >> process model. >> >> The real question here is: are we going to make system scope thread >> model fair compared to process scope threaded model, or fair compared >> to the separate processes model? >> >> Yes, the process scope threads are allways going to be the poor man >> with regard to priority, but as the kernel doesn't see the threads you >> can't do much about it. > > I think there are at least two core questions being discussed here: > > (1) Does the "fairness" model currently implemented in the KSE code mean > well, > but cause significant performance problems in practice for real-world > applications? > > (2) Are the cost and complexity impacts of KSE in kernel architecture > outweighed by the flexibility and performance benefits of M:N > threading? > > Now is definitely the time for us to be discussing, measuring, > experimenting, etc, because addressing the issues of higher concurrency > for 7.0 will depend on having decided on a strategy for our scheduler. > I'd like to add (3) Who is committed to maintaining and improving the M:N and KSE architectures for the long term? THR and 1:1 has an active and committed maintainer right now, KSE does not. Whether KSE is 'better' is purely academic if no one is willing to actually make it work. Scott
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