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Date: Thu, 19 May 2011 19:58:00 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: Attilio Rao <attilio@FreeBSD.org>, Garrett Cooper <yanegomi@gmail.com>
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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 18/05/2011 20:04 Attilio Rao said the following:
> 2011/5/18 Garrett Cooper <yanegomi@gmail.com>:
>> We use this internally at work still with a software config that uses 4BSD so
>> as long as there is an equivalent tunable, that's good enough for us moving
>> forward.

Can you please clarify which exactly tunable(s) do you use/need?
Just turning hyperthreading on/off or more?  (BTW, doing that via BIOS is
inconvenient / not feasible?)

BTW, I think that if we switch hyperthreading off then we better off not sending
Start IPI to the logical CPUs at all.

> Tunables are pretty much acceptable for this case. What is really broken is the
> on-the-fly ability to mark CPUs active/inactive and subsequent handovers.

Yes, I completely agree.  Static disabling of CPUs doesn't have any problems, and
IMO, currently the best way to do it is with hint.lapic.X.disabled.

> I thought Andriy attached a patch to the tree, but it doesn't seem so...
> anyway, yes, I think that adding tunables for this is very reasonable and not
> as dangerous as the current mechanism.

I agree.
I haven't sent a patch, because I don't have it yet :)
I decided to solicit opinions before getting to hacking code.

-- 
Andriy Gapon