Re: [PATCH 01/70] cpufreq: interactive: New 'interactive' governor

From: Rafael J. Wysocki
Date: Tue Oct 27 2015 - 20:30:11 EST


On Tuesday, October 27, 2015 06:29:49 PM BÃlint Czobor wrote:
> From: Mike Chan <mike@xxxxxxxxxxx>
> This governor is designed for latency-sensitive workloads, such as
> interactive user interfaces. The interactive governor aims to be
> significantly more responsive to ramp CPU quickly up when CPU-intensive
> activity begins.
> Existing governors sample CPU load at a particular rate, typically
> every X ms. This can lead to under-powering UI threads for the period of
> time during which the user begins interacting with a previously-idle system
> until the next sample period happens.
> The 'interactive' governor uses a different approach. Instead of sampling
> the CPU at a specified rate, the governor will check whether to scale the
> CPU frequency up soon after coming out of idle. When the CPU comes out of
> idle, a timer is configured to fire within 1-2 ticks. If the CPU is very
> busy from exiting idle to when the timer fires then we assume the CPU is
> underpowered and ramp to MAX speed.
> If the CPU was not sufficiently busy to immediately ramp to MAX speed, then
> the governor evaluates the CPU load since the last speed adjustment,
> choosing the highest value between that longer-term load or the short-term
> load since idle exit to determine the CPU speed to ramp to.
> A realtime thread is used for scaling up, giving the remaining tasks the
> CPU performance benefit, unlike existing governors which are more likely to
> schedule rampup work to occur after your performance starved tasks have
> completed.
> The tuneables for this governor are:
> /sys/devices/system/cpu/cpufreq/interactive/min_sample_time:
> The minimum amount of time to spend at the current frequency before
> ramping down. This is to ensure that the governor has seen enough
> historic CPU load data to determine the appropriate workload.
> Default is 80000 uS.
> /sys/devices/system/cpu/cpufreq/interactive/go_maxspeed_load
> The CPU load at which to ramp to max speed. Default is 85.
> Change-Id: Ib2b362607c62f7c56d35f44a9ef3280f98c17585
> Signed-off-by: Mike Chan <mike@xxxxxxxxxxx>
> Signed-off-by: Todd Poynor <toddpoynor@xxxxxxxxxx>
> Bug: 3152864
> Signed-off-by: BÃlint Czobor <czoborbalint@xxxxxxxxx>

It's good to see that submitted, but it'll have to go through a detailed
review which is going to take some time.

One my observation after a cursory look at it is that at least some later
patches of the series modify drivers/cpufreq/cpufreq_interactive.c which is
a new file added by the first patch. Is there any particular reason to
avoid folding all of those patches into the first one?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at