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authorThomas Renninger <trenn@suse.de>2009-02-04 01:17:41 +0100
committerDave Jones <davej@redhat.com>2009-02-24 22:47:31 -0500
commited12978453a3845c947695e7ad32bb3ede444813 (patch)
tree6fcec1eaa023fd2cadce8e82a17b9b890f59fd88 /Documentation/cpu-freq
parent0e64a0c982c06a6b8f5e2a7f29eb108fdf257b2f (diff)
downloadkernel-ed12978453a3845c947695e7ad32bb3ede444813.tar.gz
[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: Thomas Renninger <trenn@suse.de> Signed-off-by: Dave Jones <davej@redhat.com>
Diffstat (limited to 'Documentation/cpu-freq')
-rw-r--r--Documentation/cpu-freq/user-guide.txt12
1 files changed, 12 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/user-guide.txt b/Documentation/cpu-freq/user-guide.txt
index 917918f84fc7..75f41193f3e1 100644
--- a/Documentation/cpu-freq/user-guide.txt
+++ b/Documentation/cpu-freq/user-guide.txt
@@ -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