I/O APIC, one of intel's interrupt controllers, can only change the
affinity on an IRQ line during an EOI (end of interrupt)[1]. In other
words, on boot, although tuned will set a preferred IRQ affinity, it
might not be applied until the next time the interrupt is triggered.
This might be right away, or hours later while oslat or a
latency-sensitive workload is running.
To mitigate this set the 'irqaffinity='kernel command-line[2] option to
match the non-isolated CPU mask when running the realtime-virtual-*
profiles. This way we'll get the right affinity regardless of the
situation stated above.
[1] For more reference see kernel's ioapic_ack_level() function and the
IRQD_SETAFFINITY_PENDING flag.
[2] Actually, this is why irqaffinity was introduced in the first place,
see kernel commit fbf198030e0b0.
Resolves: rhbz#1974820
Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
288ac9ba9d