Date: Fri, 21 Dec 2007 16:26:06 +0800 From: David Xu <davidxu@FreeBSD.org> To: Daniel Eischen <deischen@FreeBSD.org> Cc: freebsd-threads@FreeBSD.org Subject: Re: threads/118910: Multithreading problem Message-ID: <476B789E.4040009@freebsd.org> In-Reply-To: <Pine.GSO.4.64.0712210310090.20251@sea.ntplx.net> References: <200712210700.lBL707MZ002071@freefall.freebsd.org> <Pine.GSO.4.64.0712210228030.20251@sea.ntplx.net> <476B6E35.508@freebsd.org> <Pine.GSO.4.64.0712210243120.20251@sea.ntplx.net> <476B7476.3010509@freebsd.org> <Pine.GSO.4.64.0712210310090.20251@sea.ntplx.net>
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Daniel Eischen wrote: > On Fri, 21 Dec 2007, David Xu wrote: > >> Daniel Eischen wrote: >> >>> I don't think it is as big a change as you think it is. We already >>> have several layers of priorities (interrupt, time-share, idle, ?). >>> All threads belong to these classes. As long as priority inheritence >>> works, there should be no problems. The problems seem to occur when >>> we try to inject artificial priorities into threads, like using >>> msleep(). I think we are better off just letting threads run based >>> on their own base priority and whatever their inherited priority is. >>> >> >> For test purpose, you may try to ignore thread priority parameter >> in msleep(), I didn't test this, but it does change the FreeBSD >> behavior. I don't know any side effect since I am unable to test >> all applications in the world, maybe you can start a project to hack >> it ? > > I'll take a look at trying that. I should be able to figure out > how to get msleep to ignore the priority. But I think the missing > piece is the interrupt routines - they need to create their mutexes > and CVs so that they are more like priority ceiling mutexes. Any > thread (even non-interrupt threads) that takes one of these mutexes > needs to have its priority raised as well as blocking the interrupt > (for fast interrupts anyway) until the mutex is released. > kernel mutex is already priority inheritence, the spin lock mutex looks like a priority protected mutex which raises thread priority to highest possible(critical section), and can not be preempted. so there is no priority problem in mutex. The only problem I can think of is semaphore-like msleep/wakeup pair which does not do priority inheritance, if a higher priority thread is blocked in msleep, priority of another thread holding the resources is not boosted.
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