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x86: New (un)idle IPIs for setting idle flag in scheduler
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Authored by obiwac on Dec 29 2025, 8:59 PM.
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Reviewers
olce
markj
Summary

For s2idle, we need a reliable way to force the scheduler into an idle loop. This adds IPIs we can send to specific CPU sets to idle or unidle them.

If I were 100% sure the CPUs wouldn't get any other kinds of IPIs during the s2idle loop, we could probably do away with the extra unidle IPI and just "kick" the CPUs with a preempt or something to clear their scheduler idle flags. But for now this guarantees things will work.

This is a bit heavy-handed and not necessarily the right approach - revision opened mostly so @olce can have a look :)

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rG FreeBSD src repository
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Buildable 69513
Build 66396: arc lint + arc unit

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Can totally use smp_rendezvous_cpus() for this instead of adding 2 new IPIs. I thought I had run into a problem using rendezvous when I first implemented this, but I just tried it again and see no problem doing it this way.

Can totally use smp_rendezvous_cpus() for this instead of adding 2 new IPIs. I thought I had run into a problem using rendezvous when I first implemented this, but I just tried it again and see no problem doing it this way.

So this is as we discussed. Great.