On 06/18/2012 02:53 PM, Peter De Schrijver wrote: > On Mon, Jun 18, 2012 at 02:35:42PM +0200, Daniel Lezcano wrote: >> On 06/18/2012 01:54 PM, Deepthi Dharwar wrote: >>> On 06/18/2012 02:10 PM, Daniel Lezcano wrote: >>> >>>> >>>> Dear all, >>>> >>>> A few weeks ago, Peter De Schrijver proposed a patch [1] to allow per >>>> cpu latencies. We had a discussion about this patchset because it >>>> reverse the modifications Deepthi did some months ago [2] and we may >>>> want to provide a different implementation. >>>> >>>> The Linaro Connect [3] event bring us the opportunity to meet people >>>> involved in the power management and the cpuidle area for different SoC. >>>> >>>> With the Tegra3 and big.LITTLE architecture, making per cpu latencies >>>> for cpuidle is vital. >>>> >>>> Also, the SoC vendors would like to have the ability to tune their cpu >>>> latencies through the device tree. >>>> >>>> We agreed in the following steps: >>>> >>>> 1. factor out / cleanup the cpuidle code as much as possible >>>> 2. better sharing of code amongst SoC idle drivers by moving common bits >>>> to core code >>>> 3. make the cpuidle_state structure contain only data >>>> 4. add a API to register latencies per cpu >>> >>> On huge systems especially servers, doing a cpuidle registration on a >>> per-cpu basis creates a big overhead. >>> So global registration was introduced in the first place. >>> >>> Why not have it as a configurable option or so ? >>> Architectures having uniform cpuidle state parameters can continue to >>> use global registration, else have an api to register latencies per cpu >>> as proposed. We can definitely work to see the best way to implement it. >> >> Absolutely, this is one reason I think adding a function: >> >> cpuidle_register_latencies(int cpu, struct cpuidle_latencies); >> >> makes sense if it is used only for cpus with different latencies. >> The other architecture will be kept untouched. >> >> IMHO, before adding more functionalities to cpuidle, we should cleanup >> and consolidate the code. For example, there is a dependency between >> acpi_idle and intel_idle which can be resolved with the notifiers, or >> there is intel specific code in cpuidle.c and cpuidle.h, cpu_relax is >> also introduced to cpuidle which is related to x86 not the cpuidle core, >> etc ... >> >> Cleanup the code will help to move the different bits from the arch >> specific code to the core code and reduce the impact of the core's >> modifications. That should let a common pattern to emerge and will >> facilitate the modifications in the future (per cpu latencies is one of >> them). >> >> That will be a lot of changes and this is why I proposed to put in place >> a cpuidle-next tree in order to consolidate all the cpuidle >> modifications people is willing to see upstream and provide better testing. > > Sounds like a good idea. Do you have something like that already? Yes but I need to cleanup the tree before. http://git.linaro.org/gitweb?p=people/dlezcano/linux-next.git;a=summary -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog
