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SubjectCPU hotplug and IRQ affinity with 2.6.24-rt1
This is just an FYI. As part of the "Isolated CPU extensions" thread Daniel suggest for me
to check out latest RT kernels. So I did or at least tried to and immediately spotted a couple
of issues.

The machine I'm running it on is:
HP xw9300, Dual Opteron, NUMA

It looks like with -rt kernel IRQ affinity masks are ignored on that system. ie I write 1 to
lets say /proc/irq/23/smp_affinity but the interrupts keep coming to CPU1.
Vanilla 2.6.24 does not have that issue.

Also the first thing I tried was to bring CPU1 off-line. Thats the fastest way to get irqs,
soft-irqs, timers, etc of a CPU. But the box hung completely. It also managed to mess up my
ext3 filesystem to the point where it required manual fsck (have not see that for a couple of
years now).
I tried the same thing (ie echo 0 > /sys/devices/cpu/cpu1/online) from the console. It hang
again with the message that looked something like:
CPU1 is now off-line
Thread IRQ-23 is on CPU1 ...
IRQ 23 is NVidia SATA. So I guess it has something to do with the borked affinity handling.
Vanilla 2.6.24 handles this just fine.

Anyway, like I said it's just an FYI, not an urgent issue.

Max



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