On 10/11/2016 02:13 πμ, Rafael J. Wysocki wrote: > On Wed, Nov 9, 2016 at 6:55 AM, Viresh Kumar <viresh.ku...@linaro.org> wrote: >> On 08-11-16, 21:25, Stratos Karafotis wrote: >>> But this is the supposed behaviour of conservative governor. We want >>> the CPU to increase the frequency in steps. The patch just resets >>> the frequency to a lower frequency in case of idle. >>> >>> For argument's sake, let's assume that the governor timer is never >>> deferred and runs every sampling period even on completely idle CPU. >> >> There are no timers now :) >> >>> And let's assume, for example, a burst load that runs every 100ms >>> for 20ms. The default sampling rate is also 20ms. >>> What would conservative do in case of that burst load? It would >>> increase the frequency by one freq step after 20ms and then it would >>> decrease the frequency 4 times by one frequency step. Most probably >>> on the next burst load, the CPU will run on min frequency. >>> >>> I agree that maybe this is not ideal for performance but maybe this is >>> how we want conservative governor to work (lazily increase and decrease >>> frequency). >> >> Idle periods are already accounted for while calculating system load by >> legacy >> governors. >> >> And the more and more I think about this, I am inclined towards your patch. >> Maybe in a bit different form and commit log. >> >> If we see how the governors were written initially, there were no deferred >> timers. And so even if CPUs were idle, we will wake up to adjust the step. >> >> Even if we want to make the behavior similar to that, then also we should >> account of missed sampling periods both while decreasing or increasing >> frequencies. >> >> @Rafael: What do you think ? > > It looks like the issue with the conservative governor is real, but > I'm a bit concerned about adding things to use by one particular > governor only to cpufreq_governor.c.
I think the code is minimum and I didn't find a way to do this calculation in cpufreq_conservative.c. We also use code in cpufreq_governor.c that it's only specific to ondemand (io_busy). If you can give me a hint about how to implement this logic in cpufreq_conservative I would appreciate it. > Apart from the timer-related terminology that is not applicable any > more, of course. I will correct the terminology if the logic is accepted. Regards, Stratos