linux-kernel - Re: [RFC V1] cpuidle: add idle routine registration and cleanup pm

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Message-ID: <AANLkTimNWYuP0e03xTq4Yg7Sb1RPHsQjC2X4wpf1CcPB@mail.gmail.com>
Date:	Wed, 20 Oct 2010 12:47:22 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	svaidy@...ux.vnet.ibm.com, Andi Kleen <ak@...ux.intel.com>,
	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>,
	peterz@...radead.org, lenb@...nel.org, suresh.b.siddha@...el.com,
	benh@...nel.crashing.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC V1] cpuidle: add idle routine registration and cleanup
 pm_idle pointer

On Wed, Oct 20, 2010 at 12:44 PM, Arjan van de Ven
<arjan@...ux.intel.com> 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.

Thanks,
Venki
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