Messages in this thread | | | Date | Wed, 18 Jul 2012 17:18:54 +0530 | From | Deepthi Dharwar <> | Subject | Re: [PATCH 1/1] Honor state disabling in the cpuidle ladder governor |
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On 07/18/2012 04:32 PM, Carsten Emde wrote:
> 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.
Agree, as per the ladder design.
> 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? >
No, I dont think thats necessary, current code suffices it. The disable flag is knob we are giving to the user . So may be just document the intended use of disable flag working alongside design of ladder governor.
Cheers Deepthi
> -Carsten. >
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