[1595] in linux-scsi channel archive
Re: Shared interrupts for ncr8xx?
daemon@ATHENA.MIT.EDU (Gerard Roudier)
Sun Mar 23 13:42:57 1997
Date: Sun, 23 Mar 1997 19:39:13 +0000 (GMT)
From: Gerard Roudier <groudier@club-internet.fr>
To: David Gray <davidg@newton.dialix.com.au>
cc: linux-scsi@vger.rutgers.edu
In-Reply-To: <33355F2F.1395ED39@newton.dialix.oz.au>
David,
On Mon, 24 Mar 1997, David Gray wrote:
> Hi,
>
> Pardon me if this is a FAQ...
>
> Can someone confirm whether PCI interrupt sharing is supported in the
> ncr53c8xx scsi drivers? I want to put 810 and 875 based cards in a
> machine together. There is mention of it in the README.ncr53c8xx file in
> the 2.0.29 kernel distribution, but it doesn't seem to commit either
> way. Are there any performance issues with interrupt sharing?
Sharing interrupt is supported in the ncr53c8xx driver, so:
- Severall NCR53C8XX boards can share the same interrupt.
- Any NCR53C8XX board can share the same interrupt with any other PCI
board if both are using level triggered interrupt line.
However, all the drivers involved must have requested the interrupt to
the kernel as *shareable*.
When a shared interrupt raised, the kernel has to call all the interrupt
routines that have been assigned to this interrupt.
Each interrupt routine must look at some hardware specific interrupt
status in order to check if it has to service the interrupt. If not,
it shall return immediately.
In my opinion, sharing an interrupt among 2 or 3 boards does not make
significant overload. However, my advice is to avoid interrupt sharing
if it is possible (i.e. you've enough available #INTs for all your boards).
> Please reply directly to me and I will summarise to the list if there is
> other interest. I am happy to supply more detail (card / system details)
> if required.
I use a 875 and a 810A on my personnal system, but still have enough
interrupts available for each boards and so I did not need to share a
single interrupt for the both boards.
Gerard.
