Messages in this thread | | | Date | Thu, 9 Oct 2014 19:38:23 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH RFC 2/2] cpufreq: arm_big_little: provide cpu capacity |
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On Thu, Oct 09, 2014 at 10:25:13AM -0700, Mike Turquette wrote: > Quoting Peter Zijlstra (2014-10-09 02:02:52) > > On Wed, Oct 08, 2014 at 03:37:32PM -0700, Mike Turquette wrote: > > > It creates a dependency such that any ARM platform that wants to have > > > frequency-invariant load must use CPUfreq. I don't think we want that > > > dependency. CPUfreq is a likely back-end for many devices, but not all. > > > > > > Consider near-future ARM devices that support ACPI for power management > > > with no corresponding CPUfreq driver. For example if the CPPC driver is > > > not hooked up to CPUfreq, platforms using CPPC will not jive with the > > > ARM arch hook that depends on CPUfreq. > > > > Oh crap no, CPPC will not add yet another interface to cpu frequency > > stuff. > > Right. > > So let's say the ARM arch hook creates a dependency on CPUfreq to scale > capacity as a function of cpu frequency (as it does in the ARM scale > invariance series). > > Then let's say that a hypothetical ARM platform named "foo" uses CPPC > and not CPUfreq to scale frequency. Foo's implementation of CPPC does > not use any of the full-auto or hw-auto stuff. It allows the OS to > request minimum performance levels and the like. > > In this case, how can foo take advantage of the scale invariant stuff? > > Also, feel free to replace "CPPC" with "anything other than CPUfreq". > The problem is a general one and not specific to CPPC or ACPI.
Well answer #1 is that you simply should not ever bypass cpufreq for setting cpu frequencies (be this the existing cpufreq or the future integrated cpufreq).
Answer #2 is that if you were allowed to create a second infrastructure and you're not calling the right scheduler hooks right along with it, you're buggy.
In short, your problem, not mine.
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