Date: Sat, 25 Oct 1997 23:09:32 +0200 From: Stefan Esser <se@FreeBSD.ORG> To: dkelly@hiwaay.net Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: ncr53c875j under FreeBSD-2.2.2 Message-ID: <19971025230932.41623@mi.uni-koeln.de> In-Reply-To: <199710251831.NAA08387@nospam.hiwaay.net>; from dkelly@HiWAAY.net on Sat, Oct 25, 1997 at 01:31:46PM -0500 References: <se@FreeBSD.ORG> <199710251831.NAA08387@nospam.hiwaay.net>
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On 1997-10-25 13:31 -0500, dkelly@HiWAAY.net wrote: > Stefan Esser said: > > > > My guess is, that there is an IRQ conflict between PCI and ISA. Could > > verify, that none of the IRQs printed for the PCI cards is configured > > for one of your ISA cards, too. I do not know anything about your PCI > > BIOS (whether it dynamically assigns interrupts to PCI slots, for > > example), but assume some kind of configuration problem exists. > > Is it OK for PCI cards to share the same IRQ? I was thinking my Asus > SC875 and IBM DCHS-39100 were not performing up to par and found it on > IRQ 9, also the 2940 and Mach32 were all on IRQ 9. Now the performance > is up to expectations after I discovered write buffering was not > enabled on the DCHS. PCI requires all cards to support shared interrupts, while PCI chips wired onto a motherboard need not. The interrupt code in FreeBSD knows how to deal with shared interrupts, but there is some (low) additional overhead, since all cards that share an interrupt have to be polled to find the real interrupt source. If anybody observes performance problems which depend on shared interrupts, I'd like to hear about them. On one occasion, going from shared to exclusive IRQs helped performance a lot, but there may have been some configuration or setup problem. I have tried shared interrupts on my system (which does require manual assignment of IRQs to PCI slots), and found no measurable difference in performance with 2 NCR SCSI cards and one PCI NE2000 clone all using the same IRQ. Regards, STefan
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