Date: Mon, 4 Oct 2004 11:31:35 -0400 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-arch@FreeBSD.org Cc: Stephan Uphoff <ups@tree.com> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <200410041131.35387.jhb@FreeBSD.org> In-Reply-To: <1096603981.21577.195.camel@palm.tree.com> References: <1095468747.31297.241.camel@palm.tree.com> <1096496057.3733.2163.camel@palm.tree.com> <1096603981.21577.195.camel@palm.tree.com>
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On Friday 01 October 2004 12:13 am, Stephan Uphoff wrote: > On Wed, 2004-09-29 at 18:14, Stephan Uphoff wrote: > > I was looking at the MUTEX_WAKE_ALL undefined case when I used the > > critical section for turnstile_claim(). > > However there are bigger problems with MUTEX_WAKE_ALL undefined > > so you are right - the critical section for turnstile_claim is pretty > > useless. > > Arghhh !!! > > MUTEX_WAKE_ALL is NOT an option in GENERIC. > I recall verifying that it is defined twice. Guess I must have looked at > the wrong source tree :-( > This means yes - we have bigger problems! > > Example: > > Thread A holds a mutex x contested by Thread B and C and has priority > pri(A). > > Thread C holds a mutex y and pri(B) < pri(C) > > Thread A releases the lock wakes thread B but lets C on the turnstile > wait queue. > > An interrupt thread I tries to lock mutex y owned by C. > > However priority inheritance does not work since B needs to run first to > take ownership of the lock. > > I is blocked :-( Ermm, if the interrupt happens after x is released then I's priority should propagate from I to C to B. If the interrupt happens before x is released, then the final bit of propagate_priority() should handle it since it resorts the turnstile's thread queue so that C will be awakened rather than B. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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