Date: Sun, 29 Oct 2006 09:24:14 +0000 (GMT) From: Robert Watson <rwatson@FreeBSD.org> To: Lucas James <Lucas.James@ldjcs.com.au> Cc: freebsd-current@freebsd.org Subject: Re: Comments on the KSE option Message-ID: <20061029090945.P27107@fledge.watson.org> In-Reply-To: <200610291257.11744.Lucas.James@ldjcs.com.au> 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>
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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.
Robert N M Watson
Computer Laboratory
University of Cambridge
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