Date: Thu, 5 Jul 2001 17:41:35 -0500 From: Alfred Perlstein <bright@sneakerz.org> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: John Baldwin <jhb@FreeBSD.org>, Jake Burkholder <jake@FreeBSD.org>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org, Matt Dillon <dillon@earth.backplane.com>, Matthew Jacob <mjacob@feral.com>, Doug Rabson <dfr@nlsystems.com> Subject: Re: cvs commit: src/sys/sys systm.h condvar.h src/sys/kern kern_ Message-ID: <20010705174135.A79818@sneakerz.org> In-Reply-To: <200107052228.f65MSeU64741@aslan.scsiguy.com>; from gibbs@scsiguy.com on Thu, Jul 05, 2001 at 04:28:40PM -0600 References: <XFMail.010705123747.jhb@FreeBSD.org> <200107052228.f65MSeU64741@aslan.scsiguy.com>
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* Justin T. Gibbs <gibbs@scsiguy.com> [010705 17:28] wrote: > >It happens with SMP, too, not just preemption. The calls are an optimization > >to avoid problems with releasing the lock after the wakeup. The contention > >can be avoided if we release the lock before calling wakeup(), but doing that > >leaves a window open for another CPU to alter the data that the lock protects > >possibly invalidating the wakeup that then gets sent. > > This window exists anyway. The locked mutex it not passed to the woken > up thread, so there will always be a race between the woken up thread > acquiring the mutex and some other thread on some other CPU acquiring it > first and making the wakeup invalid. Y'know this sorta got me thinking about something else, shouldn't the wakeup() calls for most exclusive locks use wakeup_one? I know wakeup_one() hoses priority, but for the locks in things like vnodes and the pager locks, shouldn't we do a wakeup_one() since it is an exclusive lock? -- -Alfred Perlstein [alfred@freebsd.org] Ok, who wrote this damn function called '??'? And why do my programs keep crashing in it? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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