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Subject: Re: [PATCH 2 1/4] powerpc: drop the ability to tweak SMT mode at
 boot time
From: Scott Wood <scottwood@freescale.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Date: Tue, 9 Dec 2014 18:14:45 -0600
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Cc: linuxppc-dev@lists.ozlabs.org, Greg Kurz <gkurz@linux.vnet.ibm.com>
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On Wed, 2014-12-10 at 10:56 +1100, Michael Ellerman wrote:
> On Tue, 2014-12-09 at 15:04 -0600, Scott Wood wrote:
> > On Tue, 2014-12-09 at 15:11 +1100, Michael Ellerman wrote:
> > > On Fri, 2014-12-05 at 12:52 -0600, Scott Wood wrote:
> > > > On Fri, 2014-12-05 at 16:14 +0100, Greg Kurz wrote:
> > > > > The smt-enabled kernel parameter basically leaves unwanted cpus executing
> > > > > in firmware or wherever they happen to be. The very same applies to the
> > > > > ibm,smt-enabled DT property which is no more used by anything known. These
> > > > > are hacks that shoudn't be used in a production environment.
> > > > > 
> > > > > Quoting mpe, "there are better ways for firmware to disable SMT".
> > > > 
> > > > Those "better ways" don't apply to Freescale chips, where the OS enables
> > > > (or not) SMT without any interaction with firmware.
> > > 
> > > But how does it know there even are SMT threads? From the device tree? So
> > > just don't present the threads in the device tree?
> > 
> > The device tree is for hardware description, not configuration...
> 
> Oh please, you're quoting device tree scripture to me now?

What benefit is there to ignoring "scripture" here?  Going from an easy
to use command line option to needing to mess around with the dts file
is not a usability improvement.  If you want to make it Freescale-only,
fine.  If you want to push me to fix the problems with the
implementation, fine.

-Scott