Date: Thu, 20 Dec 2001 13:21:24 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Alfred Perlstein <bright@mu.org>, arch@FreeBSD.org, Julian Elischer <julian@elischer.org> Subject: Re: Kernel stack size and stacking: do we have a problem ? Message-ID: <XFMail.011220132124.jhb@FreeBSD.org> In-Reply-To: <2799.1008883049@critter.freebsd.dk>
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On 20-Dec-01 Poul-Henning Kamp wrote: > > Julian, doesn't this give you an ordering issue ? > > Imagine this setup > > (lots of stuff) > | > module 1 > | > module 2 > | > module 3 > > With the added information that the path through module 2 can be very > short or very long, depending on the packet contents. > > Now, module 1 sends a request down through module 2 which takes the > long path and consequently ends up being queued a module 3. We > unwind/return back up through module 2 and module 1 issues another > request which happens to take the short path through module 2 and > consequently directly calls into module 3. > > Now the two requests have been reordered without any of the modules > having any hint of this. > > The obvious ways to fix this is to continue to queue once you queue > on a module (in other words: always queue if the queue is non-empty) Hmm, I was thinking that the original request would block when it queued the request, and would be woken up when the original request was completed by the worker thread. Thus, for each producer, only one item should be in the queue at a time (plus any sub events it may create), but that multiple producers may be putting events onto the queue handled by the worker thread. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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