Re: [RFC V1] cpuidle: add idle routine registration and cleanuppm_idle pointer

[Venkatesh Pallipadi]

On Wed, Oct 20, 2010 at 1:47 PM, Arjan van de Ven <arjan@xxxxxxxxxxxxxxx> wrote:
>  On 10/20/2010 12:47 PM, Venkatesh Pallipadi wrote:
>>
>> On Wed, Oct 20, 2010 at 12:44 PM, Arjan van de Ven
>> <arjan@xxxxxxxxxxxxxxx>  wrote:
>>>
>>>  On 10/20/2010 12:40 PM, Vaid
>>>>>
>>>>> you ALWAYS have at least 2 idle handling states. The platform idle
>>>>> one and the generic busy waiting one.
>>>>> the later is needed for "I want absolutely 0 latency" cases.
>>>>
>>>> Some special overrides like idle=poll should handle this case even if
>>>> cpuidle and related registration mechanism is compiled out. The point
>>>> is that we need some flexibility even if the full framework is not
>>>> included.
>>>
>>> this is not idle=poll
>>>
>>> this is an (privileged) app or driver, at runtime, requesting a 0 usec
>>> max
>>> latency for a short or long period of time.
>>>
>>>
>>>>>> Making current cpuidle as default in kernel
>>>>>
>>>>> not "in the kernel" but "for x86".
>>>>> You're solving an x86 problem here, right?
>>>>> (the pm_idle is an x86 only problem. other architectures should be
>>>>> able to keep doing what they are doing)
>>>>> For x86, lets solve it by going to cpuidle period... and if Andi can
>>>>> find some bloat in cpuidle, lets see if the fat can be trimmed.
>>>>
>>>> Ok, you are suggesting that for x86 lets move cpuidle in kernel
>>>> always, while it can be an optional module for other archs as it
>>>> stands today.  We can slim down the cpuidle from current 7K or atleast
>>>> split some parts like governors as modules if needed.
>>>
>>> governors as modules is a total pain. modules don't solve the problem.
>>> really. it's still code you need.
>>> we have two governors today, menu and ladder
>>> menu is best on anything that is tickless
>>> ladder is useless on any tickless kernel, and likely not better than menu
>>> on
>>> non-tickless.
>>> that's it.
>>> It will be good to have other archs also follow the same cpuidle
>>
>> I don't think they have to be modules. There can be a CPUIDLE_LITE
>> which deCONFIG entire governor.c and individual governors (and
>> probably sysfs stuff as well) for archs that can only use one state at
>> any time, but still want to do config or runtime detection of one
>> state and register that state.
>
> there is no such case though; you always have at least 2 options!
> (the hardware equivalent of "hlt" and the polling option)
>

Agree. But, from arch perspective there is only hlt and CPUIDLE_LITE
can add poll and still deconfigure all but one governor, sysfs stuff
and code dealing with registering of multiple states etc for example.
I am not saying doing all this is a priority. Just saying that, if
~7KB CPUIDLE is seen as a problem for some arch which does not have
more than one kind of halt, then there are ways to trim CPUIDLE down.

Thanks,
Venki
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