2.5.69 Interrupt Latency

[Paul Fulghum <paulkf@microgate.com>]

Starting with kernel version 2.5.69, I am
encountering what appears to be increased
interrupt latency or spikes in interrupt latency.

I noticed this on two serial drivers that use programmed
I/O with FIFOs. On 2.5.68, no problems. On 2.5.69
plenty of underruns. Inspecting the driver tracing, it
does not look like lost interrupts.

I see this on 2 different machines
(one SMP server and one laptop).

There were changes involving the return type of
interrupt handlers (from void to irqreturn_t) in 2.5.69.
Could this be related?

Has anyone else seen similar results?

If I can get time, I'll try and hook up a scope
to measure the latencies precisely. I want to
check to see if this is a known problems before doing so.

-- 
Paul Fulghum, paulkf@microgate.com
Microgate Corporation, http://www.microgate.com