Re: Regarding CPU idle C states

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Thanks for the email, Eduardo. It's useful.

Basically, we'd like to save power while maintaining performance in
storage systems with domain knowledge aware algorithm. Our previous
research papers can be found here:

http://www.fsl.cs.sunysb.edu/~zhicli/#_Publications

We can now start with the patch adding sysfs entry for C states and
provide kernel support, and try to play with them in the user level.

Regards,


On Fri, Mar 30, 2012 at 2:41 AM, Valentin, Eduardo
<eduardo.valentin@xxxxxx> wrote:
> Hello Zhichao,
>
> On Thu, Mar 29, 2012 at 11:58 PM, Zhichao Li <lzcmichael@xxxxxxxxx> wrote:
>> Hi,
>>
>> I am a third year PhD student working on power management in storage
>> systems, under the Linux platform.
>
> Good :-)
>
>>
>> We are exploring CPU DVFS, and also idle CPU C states. We figured out
>> that the scheduling of CPU frequencies is exported to user level with
>> the "userspace" governor. However, it seems the multiple idle C states
>> are only scheduled in the kernel space (governors like "menu" and
>> "ladder").
>
> OK. Which kind of exploration you are performing? Any published paper
> you would like to point?
>
>>
>> We wonder whether there is any existing kernel module or existing
>> kernel patch that can export the various idle CPU C states to the user
>> level for user's control as well.  If you could guide us to such
>> code/patch, or if you have plan to do so, we'd be more than happy to
>> help you testing the code for various idle CPU C states in the user
>> level.
>
>
> Have you seen this patch?
> https://lkml.org/lkml/2012/3/5/30
>
> It's original purpose is for debugging. One can enable of disable the
> C states available. There has been some discussion about that patch
> regarding its usage for userspace based governors. But it should be
> enough for your purpose. In theory you could keep enabled only the C
> state you want to force to be reached.
>
>
>>
>> Thanks for your time. Appreciated it!
>>
>> Regards,
>>
>> --
>> Zhichao Li
>> File Systems and Storage Lab
>> Computer Science Department
>> Stony Brook University
>> _______________________________________________
>> linux-pm mailing list
>> linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
>
>
>
> --
>
> Eduardo Valentin



-- 
Zhichao Li
File Systems and Storage Lab
Computer Science Department
Stony Brook University
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