linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Date:   Mon, 17 Jul 2017 21:41:10 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     Arjan van de Ven <arjan@...ux.intel.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        paulmck@...ux.vnet.ibm.com, yang.zhang.wz@...il.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On 2017/7/17 17:21, Peter Zijlstra wrote:
> On Fri, Jul 14, 2017 at 09:03:14AM -0700, Andi Kleen wrote:
>> fast idle doesn't have an upper bound.
>>
>> If the prediction exceeds the fast idle threshold any C state can be used.
>>
>> It's just another state (fast C1), but right now it has an own threshold
>> which may be different from standard C1.
> 
> Given it uses the same estimate we end up with:
> 
> 
> Now, unless you're mister Turnbull, C2 will never get selected when
> fast_threshold > C2_threshold.
> 
> Which is wrong. If you want to effectively scale the selection of C1,
> why not also change the C2 and further criteria.
> 
That's not our intention, I think. As long as the predicted coming idle
period > threshold, we'll enter normal idle path, you can select any supported
c-states, tick can also be turned off for power saving. Any deferrable stuff
can be invoke as well because we'll sleep long enough.

Thanks,
-Aubrey