Date: Fri, 10 Dec 1999 20:15:22 -0800 From: Arun Sharma <adsharma@sharmas.dhs.org> To: Chuck Robey <chuckr@picnic.mat.net> Cc: Nate Williams <nate@mt.sri.com>, freebsd-arch@freebsd.org Subject: Re: Thread scheduling Message-ID: <19991210201522.A4535@sharmas.dhs.org> In-Reply-To: <Pine.BSF.4.10.9912102103490.16082-100000@picnic.mat.net>; from Chuck Robey on Fri, Dec 10, 1999 at 09:14:11PM -0500 References: <199912110135.SAA23495@mt.sri.com> <Pine.BSF.4.10.9912102103490.16082-100000@picnic.mat.net>
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On Fri, Dec 10, 1999 at 09:14:11PM -0500, Chuck Robey wrote: > > I wasn't suggesting a *single* thread across multiple processors (as I > think Arun asked). Yes, that would be silly. Is what I asked also silly, > as a scheduling bias, not a guarantee or a requirement? Or would it make > no real difference? This is also called gang scheduling in OS literature. From what I remember, there are two advantages to this - both of them mainly applicable to timesharing systems - Minimize the average wait time This assumes that the related threads compete for some resources and when thread A releases a resource, it makes sense to schedule thread B, which was waiting on the resource to resume immediately, without further delay - When your memory cache is warm with the data from the swap If your system is swapping under load, it makes sense to run the threads together to completion, rather than swapping data in and out repeatedly. However, such systems are not very common these days. Any performance engineer will tell you that a system that swaps will not perform. And no one cares about statistics like average wait time. You can buy a fast CPU for < $100. So I don't see any particular advantage to doing this on a system which will most probably be used as a database server or a web server. -Arun To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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