Date: Fri, 21 Jun 2002 16:25:32 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Gary Thorpe <gat7634@hotmail.com> Cc: freebsd-arch@freebsd.org Subject: Re: multiple threads for interrupts Message-ID: <3D13B5EC.D19BB1E5@mindspring.com> References: <F63IegwDE4TAs0T4szG00002082@hotmail.com>
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Gary Thorpe wrote: > Here is a link to the abstract and postscript of the papper I had originally > read: http://www.eecg.toronto.edu/parallel/pubs_abs.html#Curran_Stumm_CS > > It does not go into interrupt servicing routines (because they use a > simulator) but the results would be applicable to general thread scheduling. I'm glad that this paper has been referenced. It demonstrates that, under load, per CPU run queues are the way to go, even though it fails to do so further from the load limit boundary. I believe, however, that this can be explained and corrected. I'd point out that the "Take" algorithm is similar in its need to examine (and therefore lock) the task queues of the other processors. I'd argue that this increased contention is really equivalent to the contention you see for the global task queue approaches. This argument is supported by the following research: http://citeseer.nj.nec.com/39182.html http://citeseer.nj.nec.com/nikolopoulos99achieving.html http://citeseer.nj.nec.com/bellosa97follow.html The approach I have suggested (I guess I should call it "Put", in light of this paper) substantially eliminates all task queue contention for the normal case, and only causes contention on migration queues if there is in fact processes undergoing an active migration at the time. Migration should be, I would argue, a relatively rare event, since migrating merely because of a transient load imbalance is ineffective use of resources; it's like not debouncing a switch in an electronics design. Here are some resources on contention reduction, which demostrate the value of eliminating even a small amount of contention: http://citeseer.nj.nec.com/dandamudi99reducing.html http://citeseer.nj.nec.com/198857.html -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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