linux-kernel - Re: [RFC/PATCH] PM / Sleep: Timer quiesce in freeze state

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Date:	Wed, 29 Oct 2014 23:09:46 +0800
From:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	"linux-pm@...r.kernel.org >> Linux PM list" 
	<linux-pm@...r.kernel.org>
Subject: Re: [RFC/PATCH] PM / Sleep: Timer quiesce in freeze state

On 2014/10/29 16:21, Peter Zijlstra wrote:
> On Wed, Oct 29, 2014 at 06:46:03AM +0800, Li, Aubrey wrote:
>> On 2014/10/28 16:29, Peter Zijlstra wrote:
>>> On Tue, Oct 28, 2014 at 12:32:16PM +0800, Li, Aubrey wrote:
>>>> On 2014/10/27 15:28, Peter Zijlstra wrote:
>>>>> On Mon, Oct 27, 2014 at 02:27:27PM +0800, Li, Aubrey wrote:
>>>>>>> Now I suppose the problem is with cpu_pause() which needs IPIs to
>>>>>>> complete? Do we really need cpuidle_pause() there?
>>>>>>> cpuidle_uninstall_handlers() seems like a daft thing to call just about
>>>>>>> there.
>>>>>>
>>>>>> Please check the log of 8651f97bd951d0bb1c10fa24e3fa3455193f3548.
>>>>>> Rafael should know more this question than me.
>>>>>
>>>>> That changelog explains its complete bollocks to do it here. We _want_
>>>>> to enter and/or remain in deep idle states.
>>>>
>>>> cpuidle_resume() will be called at the end of dpm_resume_noirq(). So we
>>>> still are able to enter deep idle states after resume.
>>>
>>> cpuidle_resume is absolute crap, as is cpuidle_suspend for that matter
>>> -- in this case.
>>>
>>> The only reason we needed cpuidle_suspend is because some BIOS shat its
>>> pants when some CPUs were in higher C states while trying to do the S3
>>> thing. We're not going to use S states or BIOS calls _at_all_, so no
>>> point in kicking CPUs out of their deep C states.
>>
>> We already kicked CPUs out of their deep C states in dpm_suspend_noirq().
>>
>> We pause cpuidle in dpm_suspend_noirq() and resume cpuidle in
>> dpm_resume_noirq(), so currently we can't enter deep c-state during S
>> states. That's an intention for some buggy BIOS.
> 
> And work arounds for buggy crap hardware should not be in generic code.
> They should be in the platform drivers associated with said crap bugs.
> 
> But I think I see what you're saying, we're going through this dpm_ crap
> even for suspend to idle, which is wrong too.
> 
>> However, for freeze state, there is another intention that we want
>> always to enter the *deepest* c-state every time we enter freeze.
>> So we need cpuidle_resume() to make sure we have deep cstate  in freeze.
>>
>> So back to your question in another email,
>>
>>> I think you can simply remove them altogether, they're nonsense.
>>
>> We need them to resume cpuidle in freeze.
> 
> So you can do cpuidle_resume() before we do the stop machine dance,

I agree, this can leave the current behavior unchanged. I'll send out a
refined version soon.

> but ideally it'd all be ripped out from generic code and stuffed into
> the platform drivers where it belongs. But at the very least it should
> be isolated to the S3 path, I bet suspend to disk doesn't care either.
> 
I think this is a good question to Rafael, which I ever asked before.

Thanks,
-Aubrey
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