Messages in this thread | | | Date | Wed, 18 Jul 2012 13:02:01 +0200 | From | Carsten Emde <> | Subject | Re: [PATCH 1/1] Honor state disabling in the cpuidle ladder governor |
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On 07/18/2012 08:36 AM, Deepthi Dharwar wrote: > On 07/18/2012 12:29 AM, Carsten Emde wrote: > >> There are two cpuidle governors ladder and menu. While the ladder >> governor is always available, if CONFIG_CPU_IDLE is selected, the >> menu governor additionally requires CONFIG_NO_HZ. >> >> A particular C state can be disabled by writing to the sysfs file >> /sys/devices/system/cpu/cpuN/cpuidle/stateN/disable, but this mechanism >> is only implemented in the menu governor. Thus, in a system where >> CONFIG_NO_HZ is not selected, the ladder governor becomes default and >> always will walk through all sleep states - irrespective of whether the >> C state was disabled via sysfs or not. The only way to select a specific >> C state was to write the related latency to /dev/cpu_dma_latency and >> keep the file open as long as this setting was required - not very >> practical and not suitable for setting a single core in an SMP system. >> >> With this patch, the ladder governor only will promote to the next >> C state, if it has not been disabled, and it will demote, if the >> current C state was disabled. > > Yes, I agree that currently that disabling a particular C-state > is not reflected in working of ladder governor. This patch is needed > to fix it on ladder too. > > Also wanted to clarify on the intended implementation here, > if there are say 5 C-states on a system, disabling 2nd > state would also end by disabling all the remaining 3 deeper states too > as ladder governor enters the lightest state first, and will only move > on to the next deeper state if a idle period was long enough as > per the implementation. > If one is disabling only the deepest state, then it would > work as intended. Yes, the patch does not make the setting of the sysfs variable "disable" coherent, i.e. if one is disabling a light state, then all deeper states are disabled as well, but the "disable" variable does not reflect it. Likewise, if one enables a deep state but a lighter state still is disabled, then this has no effect.
I could implement a sanitize mechanism of the ladder governor that takes care the "disable" variables of all deeper states are set to 1, if a state is disabled, and those of all lighter states are set to 0, if a state is enabled. Do you wish me to do that?
-Carsten.
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