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? Thanks, Peter.
