Red Hat Bugzilla – Bug 436622
IOAPIC problems with interrupts on RT kernel
Last modified: 2009-03-13 14:52:28 EDT
Description of problem:
Originally seen on Dell PowerEdge 1950s with Megaraid SAS, it looks like some
configurations of multiple IOAPICs start to malfunction after some number of
interrupt cycles. On the PE1950+megasas the symptom is that the adapter stops
interrupting for request completions
Version-Release number of selected component (if applicable):
All version of RT kernel
Consistently reproduceable on PowerEdge 1950 with Megaraid SAS driver
Steps to Reproduce:
1. Boot into rt kernel on PE1950
2. run 'dd-of-death' (while true; do dd if=/dev/sda of=/dev/null; done)
3. Look for megasas console messages about waiting for outstanding commands
Box should go into a state where the disk adapter waits for command that have
already completed but completion interrupts were missed.
No missed interrupts
So far, we've only seen this on systems with multiple IOAPICS and the
misbehaving APIC is a secondary one, usually embedded in some "super I/O" part.
We currently have two workarounds:
1. a PCI quirk that recognized problematic systems and goes through some
interrupt type gyrations, changing the interrupt from level to edge triggered
temporarily. This reprogramming of the IOAPIC seems to prevent the IOAPIC from
2. Boot the system with the noapic kernel command line. This seems to work wellm
but will be problematic on large systems with lots of interrupt sources.
I think we can close this for now.