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SubjectRe: [tip: sched/core] x86, sched: Add support for frequency invariance
Quoting Giovanni Gherdovich (2020-03-31 19:11:25)
> Hello Chris,
> thank you for catching this problem and sorry for the mess.
> Until your message I wasn't aware that CPU0 can be hotplugged, but now that I
> check the feature is been there since v3.8 :/
> The code assumes cpu0 is always there and I need to fix that.
> It seems your report comes from executing an automated test suite, can you
> give me a link to the test sources and a hint on how to run it? I'd like to
> reproduce locally so that I make sure I correctly address this problem.

It's an i915 test (so expects i915 running and root access to your
machine, with the intent of breaking your machine), but the cpu
hotplugging could be extracted

since it's basically doing:
i = 0
while :; do
test -e /sys/devices/system/cpu/cpu$i/online || break

echo 0 > /sys/devices/system/cpu/cpu$i/online
sleep .1
echo 1 > /sys/devices/system/cpu/cpu$i/online

i = $[[ $i + 1 ]]

Possibly running that under perf stat to keep perf_event_open, or
something else that hooks up the perf cpu hotplug callbacks.

Hope that helps,

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