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Commit ed129784 authored by Thomas Renninger's avatar Thomas Renninger Committed by Dave Jones
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[CPUFREQ] Introduce /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_transition_latency 



It's not only useful for the ondemand and conservative governors, but
also for userspace daemons to know about the HW transition latency of
the CPU.
It is especially useful for userspace to know about this value when
the ondemand or conservative governors are run. The sampling rate
control value depends on it and for userspace being able to set sane
tuning values there it has to know about the transition latency.

Signed-off-by: default avatarThomas Renninger <trenn@suse.de>
Signed-off-by: default avatarDave Jones <davej@redhat.com>
parent 0e64a0c9

Documentation/cpu-freq/user-guide.txt

+12 −0
Original line number Diff line number Diff line
@@ -152,6 +152,18 @@ cpuinfo_min_freq : this file shows the minimum operating 
				frequency the processor can run at(in kHz) 

cpuinfo_max_freq :		this file shows the maximum operating

				frequency the processor can run at(in kHz) 

cpuinfo_transition_latency	The time it takes on this CPU to

				switch between two frequencies in nano

				seconds. If unknown or known to be

				that high that the driver does not

				work with the ondemand governor, -1

				(CPUFREQ_ETERNAL) will be returned.

				Using this information can be useful

				to choose an appropriate polling

				frequency for a kernel governor or

				userspace daemon. Make sure to not

				switch the frequency too often

				resulting in performance loss.

scaling_driver :		this file shows what cpufreq driver is

				used to set the frequency on this CPU

drivers/cpufreq/cpufreq.c

+3 −0
Original line number Diff line number Diff line
@@ -452,6 +452,7 @@ static ssize_t show_##file_name \ 


show_one(cpuinfo_min_freq, cpuinfo.min_freq);

show_one(cpuinfo_max_freq, cpuinfo.max_freq);

show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);

show_one(scaling_min_freq, min);

show_one(scaling_max_freq, max);

show_one(scaling_cur_freq, cur);
@@ -659,6 +660,7 @@ __ATTR(_name, 0644, show_##_name, store_##_name) 
define_one_ro0400(cpuinfo_cur_freq);

define_one_ro(cpuinfo_min_freq);

define_one_ro(cpuinfo_max_freq);

define_one_ro(cpuinfo_transition_latency);

define_one_ro(scaling_available_governors);

define_one_ro(scaling_driver);

define_one_ro(scaling_cur_freq);
@@ -672,6 +674,7 @@ define_one_rw(scaling_setspeed); 
static struct attribute *default_attrs[] = {

	&cpuinfo_min_freq.attr,

	&cpuinfo_max_freq.attr,

	&cpuinfo_transition_latency.attr,

	&scaling_min_freq.attr,

	&scaling_max_freq.attr,

	&affected_cpus.attr,