Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings

From	Mark Rutland <mark.rutland@arm.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings
Date	2015-12-15 19:20 +0100
Message-ID	<qG2mB-7LE-3@gated-at.bofh.it> (permalink)
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On Tue, Dec 15, 2015 at 05:45:16PM +0000, Mark Brown wrote:
> On Tue, Dec 15, 2015 at 05:28:37PM +0000, Mark Rutland wrote:
> > On Tue, Dec 15, 2015 at 05:17:13PM +0000, Mark Brown wrote:
> 
> > > Obviously people are going to get upset if we introduce performance
> > > regressions - but that's true always, we can also introduce problems
> > > with numbers people have put in DT.  It seems like it'd be harder to
> > > manage regressions due to externally provided magic numbers since
> > > there's inherently less information there.
> 
> > It's certainly still possible to have regressions in that case. Those
> > regressions would be due to code changes in the kernel, given the DT
> > didn't change.
> 
> > I'm not sure I follow w.r.t. "inherently less information", unless you
> > mean trying to debug without access to that DTB?
> 
> If what the kernel knows about the system is that it's got a bunch of
> cores with numbers assigned to them then all it's really got is those
> numbers.  If something changes that causes problems for some systems
> (eg, because the numbers have been picked poorly but in a way that
> happened to work well with the old code) that's not a lot to go on, the
> more we know about the system the more likely it is that we'll be able
> to adjust the assumptions in whatever new thing we do that causes
> problems for any particular systems where we run into trouble.

Regardless of where the numbers live (DT or kernel), all we have are
numbers. I can see that changing the in-kernel numbers would be possible
when modifyign the DT is not, but I don't see how that gives you more
information.

Mark.
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Thread

Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-14 13:40 +0100
  Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-14 18:00 +0100
    Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-15 13:30 +0100
      Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-15 14:50 +0100
        Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 15:10 +0100
          Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-15 15:30 +0100
            Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 16:00 +0100
              Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-15 16:40 +0100
          Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-15 16:10 +0100
            Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 16:40 +0100
              Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-15 16:50 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 17:00 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Catalin Marinas <catalin.marinas@arm.com> - 2015-12-15 17:30 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 17:50 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 18:10 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 18:20 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 18:50 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 19:40 +0100
              Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-15 18:20 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 18:30 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-15 18:50 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Rutland <mark.rutland@arm.com> - 2015-12-15 19:20 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Mark Brown <broonie@kernel.org> - 2015-12-15 19:50 +0100
                Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity  bindings Juri Lelli <juri.lelli@arm.com> - 2015-12-17 10:10 +0100
      Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings Vincent Guittot <vincent.guittot@linaro.org> - 2015-12-15 15:00 +0100

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