Messages in this thread | | | Date | Tue, 14 Feb 2012 15:20:46 -0800 | From | Saravana Kannan <> | Subject | Re: [PATCH RFC 0/4] Scheduler idle notifiers and users |
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On 02/11/2012 06:45 AM, Ingo Molnar wrote: > > * Saravana Kannan<skannan@codeaurora.org> wrote: > >> When you say accommodate all hardware, does it mean we will >> keep around CPUfreq and allow attempts at improving it? Or we >> will completely move to scheduler based CPU freq scaling, but >> won't try to force atomicity? Say, may be queue up a >> notification to a CPU driver to scale up the frequency as soon >> as it can? > > I don't think we should (or even could) force atomicity - we > adapt to whatever the hardware can do.
May be I misread the emails from Peter and you, but it sounded like the idea being proposed was to directly do a freq change from the scheduler. That would force the freq change API to be atomic (if it can be implemented is another issue). That's what I was referring to when I loosely used the terms "force atomicity".
> But the design should be directed at systems where frequency > changes can be done in a reasonably fast manner. That is what he > future is - any change we initiate today takes years to reach > actual products/systems.
As long as the new design doesn't treat archs needing schedulable context to set freq as a second class citizen, I think we would all be happy. Because it's not just a matter of it being old hardware. Sometimes the decision to let the SW do the voltage scaling also comes down to HW cost. Considering Linux runs on such a wide set of archs, I think we shouldn't treat the need for schedulable context for freq setting as "broken" or "not sane".
>> IMHO, I think the problem with CPUfreq and its dynamic >> governors today is that they do a timer based sampling of the >> CPU load instead of getting some hints from the scheduler when >> the scheduler knows that the load average is quite high. > > Yes - that is one of the "frequency changes are slow" > assumptions - which is wrong.
Thanks, Saravana
-- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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