Date: Wed, 20 Oct 2004 13:23:42 -0700 From: Julian Elischer <julian@elischer.org> To: Stephan Uphoff <ups@tree.com> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: wakeup/sleep handoff. Message-ID: <4176C94E.3000700@elischer.org> In-Reply-To: <1098237638.15834.105.camel@palm.tree.com> References: <41759681.1060700@elischer.org> <1098237638.15834.105.camel@palm.tree.com>
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Stephan Uphoff wrote: >On Tue, 2004-10-19 at 18:34, Julian Elischer wrote: > > >>Is there a need to be able to somehow implement a 'wakeup_one()' that >>as part of its semantic is that the woken thread will run immediatly, >>(as in preemprion), >>and the old thread will sleep? With preemption, the old thread is left >>in the run queue, >>and after the other thread has completed, it will >>run again and probably go away and sleep for some reason.. (or at least >>go do some work that isn't >>necessarily required..) >> >>Something like handover(wakeupchan, sleepchan, msleep_args...). >> sort of an atomic wakeup/msleep. >> >>This would be used in places where work used to be done by the same >>thread, but is now done >>by a server thread.. >> >>An example would be kicking off a geom thread, when in the past we would >>have gone all >>the way down to the hardware ourself. we want to get as close to acting >>like we are still >>going all the way done as we can (performance wise). We may get some >>efficiency by >>letting the sleep system, and scheduler know what we are trying to do. >>Possibly with some >>priority inherritance implications.. (if we have a high priority, we >>probably want to ensure that the >>worker thread is run with at least that priority.) >> >> > >Why not just give the geom thread a high priority? >This, full preemption and changing a few functions to guaranty that the >highest priority thread will always run should do what you want. >( And maybe always raising the priority of threads working in the >kernel) >Actually this is relatively high on my to do list and I should have some >patches to try out in a week or two. > yessss but after the preemption (which is invisible to the caller of setrunqueue/wakeup) that thread continues on to do it's "check for completion/sleep".. it would be more efficient in my book to have an official way to hand over to a designated worker all in one hit.. You could then optimise such cases.. They are often in required fast-paths. > > Stephan > >
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