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Date: Sun, 16 Dec 2018 09:27:46 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: Barry Kauler <bkauler@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
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        Kees Cook <keescook@chromium.org>, stable@vger.kernel.org
Subject: Re: SCHEDL_SMT forced on!
Message-ID: <20181216082746.GB29097@kroah.com>
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On Sun, Dec 16, 2018 at 02:21:55PM +0800, Barry Kauler wrote:
> Mr Gleixner,
> I was upset when I compiled 4.14.87 found that SCHED_SMT had been
> forced on. At the time, I just reported it to my blog, and posted a
> question about it to a couple of forums, and stayed with an earlier
> kernel.
> 
> However, when 4.14.88 came out, and still the same situation, alarm
> bells went off, and I looked through the kernel changelog. Found it,
> 4.14.86:
> 
> "x86/Kconfig: Select SCHED_SMT if SMP enabled"
> 
> Then:
> 
> "CONFIG_SCHED_SMT is enabled by all distros, so there is not a real point to
>     have it configurable. ..."
> 
> ...that is a lie. It would be correct to state that is true of the
> distros you use, and presumably also for all of you guys who signed
> off on it.
> 
> Puppy Linux is an example of a distro that has mostly not had
> SCHED_SMT enabled. Ditto for most of the forks of Puppy. Two distros
> that I currently maintain, Quirky and EasyOS (easyos.org) have SMP
> enabled but not SCHED_SMT.
> 
> The difference between them is important, they should remain
> independently settable. I am so surprised that all of you guys went
> along with forcing it on.

Is having this option enabled causing a problem for you?  Does it cause
slowdowns or runtime issues?

thanks,

greg k-h