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@xxxxxxxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html