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Date: Wed, 25 May 2011 19:15:48 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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Cc: "freebsd-current@freebsd.org" <freebsd-current@FreeBSD.org>,
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Subject: Re: [rfc] remove hlt_cpus et al sysctls and related code
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on 23/05/2011 19:28 Andriy Gapon said the following:
> I propose the following path for moving forward.
> - use hint.lapic.X.disabled to disable individual CPUs by their APIC ID
> - use machdep.hyperthreading_allowed tunable to disable second logical CPU on each
> real core
> 
> The above should already work as expected.  One thing is that currently we have
> handling of machdep.hyperthreading_allowed tunable under SCHED_ULE.  I plan to
> make it unconditional.
> 
> Things to remove:
> - all the related sysctls for dynamic onlining/offlining
> - machdep.hlt_logical_cpus tunable (it duplicates hint.lapic.X.disabled)
> 
> It's possible to keep machdep.hlt_logical_cpus and just add some code to convert
> hlt_logical_cpus mask to a set of individual hint.lapic.X.disabled, but I don't
> see very much value in that.  But if there is a good reason to keep that tunable,
> I am prepared to jump through this hoop.
> 
> If no one objects to this proposal, I will provide a patch soon.

The patch is here:
http://people.freebsd.org/~avg/cpu-offline-sysctl.diff
It should implement the strategy described above.

I have mp_watchdog alone for now.  It seems to have the same issues with respect
to dynamic CPU state change.  Besides its compilation is disabled when SCHED_ULE
is enabled.  mp_watchdog is a nice idea, but I wonder if anyone actually uses it
(with success).

-- 
Andriy Gapon