Re: Interrupts are being dropped under heavy IO on -rt .

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, 10 Apr 2009, jvrao wrote:
> Qlogic driver uses MSI-EDGE interrupts by default.
> 
> On -rt kernel under heavy IO load we observed that the driver missed
> interrupts occasionally.
> 
> Missing interrupts caused spurious mailbox timeouts and path failovers.
> 
> Suspecting MSI interrupts, we disabled MSI and forcing the driver to use APIC
> interrupts (Patch attached).
> 
> With this change, our IO tests ran for extended period of time without any
> issues.
> 
> It would be interesting to see if the MSI infrastructure itself has issues on
> realtime, or it is the combination of qla2xxx/MSI.
> 
> Right now we don't have any setup to test out MSI with other adapters. Hence,
> wondering if anyone faced similar issues.

Hmm. Can we get down to the root cause of that problem instead of
applying a bandaid patch ?

If -rt has problems with MSI edge interrupts then we really need to
figure out why. If the qlogic driver has problems with the different
timings of -rt then we need to fix that one.

Thanks,

	tglx