[ccontrol] [PATCH] Documentation update for performance issues with cpufreq

Michael Neuling mikey at neuling.org
Mon Dec 19 13:01:29 EST 2005


Below is a documentation patch for an issue I've been hitting on my
laptop.  Basically, the interaction between the niced ccontrol
processes and cpufreq ondemand governor means that compiles take 2-3
times longer (on my laptop) than they need to.

Patch is against 0.7.


 ccontrol.1.txt |   10 ++++++++++
 1 files changed, 10 insertions(+)

Index: ccontrol-0.7/ccontrol.1.txt
--- ccontrol-0.7.orig/ccontrol.1.txt
+++ ccontrol-0.7/ccontrol.1.txt
@@ -206,6 +206,16 @@ The .ccontrol/default file must be writa
 an exclusive write lock on it, which means it needs to open the file
 for writing.  Use 'include' to include read-only files.
+The cpufreq ondemand governor (default for laptops) only increases the
+CPU frequency from minimum when a process of nice < 0 is running.
+ccontrol always spawns processes with nice=10, so even though a load
+of much greater than 1 often occurs, the CPU will remain at the
+minimum frequency.  This can result in a significant performance hit
+(2-3 times slower in some cases).  To get around this, use another
+governor (eg. performance) or get the ondemand governor to ignore the
+nice setting using the following (as root):
+  echo 1 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice
 If your code doesn't compile, ccontrol can only make it not compile

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