Date: Mon, 28 Feb 2005 00:26:10 -0800 From: Julian Elischer <julian@elischer.org> To: Ashwin Chandra <ashcs@ucla.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: sched_4BSD Message-ID: <4222D5A2.9010301@elischer.org> In-Reply-To: <001a01c51d6d$d50ce500$abe243a4@ash> References: <001a01c51d6d$d50ce500$abe243a4@ash>
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Ashwin Chandra wrote: > I wanted to get some clarification about the 4BSD scheduler. I am sort of > confused why there are two forms of scheduling, one done between processes and > another done between threads in a process. The priority calculations seem to be > done only with processes and I assume that the global run queue holds processes, > not threads. Also why is there only 1 run queue for 1 CPU. What happens to > blocked processes and ready to be runned processes? Part of the challenge of adding threads to a system is to make it hard for a threaded process to "flood" the system run queues so that other processes get no cpu time. The scheme in the current freeBSD schedulers is a "crude" method, by which only a limitted number of threads per process are allowed to be added to the system run queue. RUnnable hreads fo r aprocess are kept on a run queue for the process and only the highest N prioriy hreads are actually put on the system run queue. This is by no means the best way, but rather the easiest way. I am hoping that some PhD candidate somewhere will decide that thread scheduling is his topic and will figure out a better way of doing this. both run queues hold threads. This is still a place wjere a lot of work can be done. :-) > > Ash > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org"
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