Re: Performance counter API review was [patch] Performance Countersfor Linux, v3

[Nathan Lynch]

Paul Mackerras wrote:
>
> By the way, how does userspace get to know about cpus being added or
> removed?  Is there a better way than continually reading
> /sys/devices/system/cpu/online?

The kernel generates uevents for cpu online and offline operations;
you can see them with udevmonitor.  Not sure how you get those events
to an arbitrary application, though.  Alternatively you can set an
inotify watch on e.g. /sys/devices/system/cpu/cpu1/online (at least it
seems to work here).
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