Re: MMIO ioremap() error with PCI passthrough

[Andy Burns <lists.xensource.com@adslpipe.co.uk>]

On 01/07/2008 20:57, Keir Fraser wrote:

> Interrupt sharing generally depends on which lines are
> wired together on your mainboard. When Xen receives an interrupt on a shared
> line it does not have enough information to demultiplex that interrupt to
> the appropriate receiver -- it has to broadcast to all potential recipients.

OK.

Sucking data at several Mb/s from a tv tuner, then squirting it to disk, 
where the tuner and disk are sharing the same interrupt doesn't sound 
ideal then ;-)

The SATA controller is presently performing an online mdraid reshape 
from 6 to 8 disks, averaging 6000 interrupts per second, so that's 
probably what is triggering the 99,900 "ignored" interrupts in 40 seconds!

> I have no idea what IOAPIC[1] above really represents. Usually the GSI range
> for an IOAPIC corresponds to its array of interrupt input pins. I've never
> heard of a 256-pin IOAPIC!

Could it relate to MSI?

> The best you could hope for would be to try out the MSI/MSI-X support in the
> xen-unstable tree (soon to be Xen 3.3). These are message-based interrupts
> which completely sidesteps the issue of interrupt lines and their wiring
> together.

Sounds good, but I gather it's only for PCIe or PCI2.3 devices, so my 
present tuners won't directly benefit, I suppose they might benefit 
indirectly by other devices using MSI and freeing up hardwired 
interrupts rather than being shared. Longer term I'll probably get a 
PCIe dual tuner.

Thanks for you help today, it'll likely be the weekend before I can look 
into this any further.