Date: Mon, 7 Mar 2005 03:34:58 -0800 (PST) From: "Kamal R. Prasad" <kamalpr@yahoo.com> To: Steve Watt <steve@Watt.COM> Cc: hackers@freebsd.org Subject: Re: sched_4BSD Message-ID: <20050307113458.7711.qmail@web52705.mail.yahoo.com> In-Reply-To: 6667
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--- Steve Watt <steve@Watt.COM> wrote: > In > <20050306101423.44745.qmail@web52702.mail.yahoo.com>, > >N)? > > "Problem"? Scheduler activations may be used to > build M:N > systems, but that is not a requirement -- you can > easily > build a 1:1 (all threads are system contention > scope) system > with activations. > But the POSIX std allows one to specify that the thread be either process scope or system scope, and if some of them are system/process scope -that leads to an M:N system. > Admittedly, at this point in industry experience, > most > threads experts will say that M:N threading usually > isn't > worth the implementation headaches. But there are Hmm -so no implementation can provide a good M:N system. [snip] > convenience. Very many processes with thousands of > threads > in them will drag down a 1:1 system pretty rapidly. > I get the idea that not everyone in the pthreads-user community is content with a 1:1 model (though I would be). [snip] > handle contention scope correctly. I don't think > anyone > has built such a system, but would be happy to be > proven > wrong -- it'd be a useful advancement of the art. Isn't a system supporting both process/system scope a POSIX requirement? BTW -the std sounds weird to me at times. They want to treat a process as a shell with a single (hypothetical) thread in it -and their scheduling classes don't have a 1:1 correspondence to the unix scheduler. SCHED_RR is a realtime scheduling class but I mistook it for a round robin scheduler:-). > One > challenge is accounting for time on threads that > don't do > much work when awakened before going back to sleep If every kernel thread were to be treated at par with a process, we wouldn't need a special algorithm. regards -kamal ------------------------------------------------------------ Kamal R. Prasad UNIX systems consultant kamalp@acm.org In theory, there is no difference between theory and practice. In practice, there is:-). ------------------------------------------------------------ __________________________________ Celebrate Yahoo!'s 10th Birthday! Yahoo! Netrospective: 100 Moments of the Web http://birthday.yahoo.com/netrospective/
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