[Xen-devel] APIC errors resulting from too early set_timer()

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

Keir,

in c/s 17422 you moved the alloc_pdata scheduler callout into the
CPU_UP_PREPARE notifier handler, but the credit scheduler uses
set_timer() for a timer bound to the to be brought up CPU from
sched_alloc_pdata(), with the resulting send_IPI_mask() targeting
the not yet started CPU, thus (on my AMD systems at least)
resulting in APIC send accept errors.

I see three possible fixes, neither really nice imo: Either a second
callout (from CPU_ONLINE), or a credit scheduler specific notifier
(handling CPU_ONLINE), or binding the timer initially to the current
CPU, and migrate it to the target CPU as soon as that one's online.

Do you favor any one of these, or do you see any alternative?

Jan


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