linux-kernel - Re: [tip: core/rcu] rcu: Enable tick for nohz

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Date:   Sat, 25 Jan 2020 21:19:05 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        x86 <x86@...nel.org>
Subject: Re: [tip: core/rcu] rcu: Enable tick for nohz_full CPUs slow to
 provide expedited QS

On Sat, Jan 25, 2020 at 11:48:46AM -0800, Paul E. McKenney wrote:
> My guess is "no" because the real-time application would not yet be
> running during boot.  On the other hand, if this issue is due not so much
> to boot, but to (say) expensive filesystem operations on large systems,
> that might be a different story.

Possible - that warn happened around a btrfs init-something.

> Except that I would have hard questions to ask of someone doing expensive
> filesystem operations while their deep-sub-millisecond real-time
> application was running.  So even then, I doubt that they would care.
> 
> Again, if I am wrong about this, this would be an excellent time for
> them to let me know.

I can see the hint there. :-)

> In the meantime, one question...  Are you testing for realtime suitability
> on your big box?  If so, to what extent?

Nah, just boot-testing tip/master before the merge window opens. Got a
couple of boxes on which I throw tip/master on from time to time and see
what breaks. I have caught a number of issues in past years, so it is a
useful exercise.

> Aside from habitually failing to trim emails, which of these was I
> violating?  ;-)

That's my mail signature. In the hope that people see that doc and stop
doing the same annoying things on LKML, it gets pasted in every mail of
mine. I didn't mean you or your mail.

:-)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette