Date: Sun, 2 May 2004 13:12:51 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: "M. Warner Losh" <imp@bsdimp.com> Cc: freebsd-current@freebsd.org Subject: Re: sio: lots of silo overflows on Asus K8V with Moxa Smartio C104H/PCI Message-ID: <20040502130027.O1806@gamplex.bde.org> In-Reply-To: <20040501.162455.37300016.imp@bsdimp.com> References: <20040426233925.Y5300@gamplex.bde.org> <20040430102504.477152ce.bm@malepartus.de> <20040501.162455.37300016.imp@bsdimp.com>
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On Sat, 1 May 2004, M. Warner Losh wrote: > In message: <20040501140658.F19558@gamplex.bde.org> > Bruce Evans <bde@zeta.org.au> writes: > : Not using a fast interrupt handler may cause occasional silo overflows, > : but shouldn't cause many. The problem is mostly elsewhere (Giant locking > : for too long), but siointr() shouldn't use Giant locking. Try the following > : patch if you still have shared interrupts: > > Is the tty layer giant safe now? No, but siointr() doesn't go near the tty layer or almost any other layer. It uses pseudo-dma and schedules a SWI to transfer data between its buffers and the tty layer. Fast interrupt handlers cannot call other layers because they cannot reasonable lock other layers or vice versa. (Even the call to the scheduler to schedule a SWI in the current implementation is a layering violation.) SImilarly for all other fast interrupt handlers if they are attached as normal interrupt handlers without changing their locking. The requirements for them to act as fast interrupt handlers are stricter than those for INTR_MPSAFE normal interrupt handlers, so fast interrupt handlers are automatically INTR_MPSAFE when downgraded to normal ones. Bruce
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