linux-kernel - Re: [RFD] Add debugfs for cpuidle ?

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Message-ID: <11155078.TUGiezxXmY@aspire.rjw.lan>
Date:   Thu, 24 May 2018 11:39:30 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [RFD] Add debugfs for cpuidle ?

On Thursday, May 24, 2018 10:47:54 AM CEST Daniel Lezcano wrote:
> On 24/05/2018 10:28, Rafael J. Wysocki wrote:
> > On Thursday, May 24, 2018 10:14:31 AM CEST Daniel Lezcano wrote:
> >> 
> >> Hi all,
> > 
> > Hi,
> > 
> >> would it be interesting to add debugfs metrics for cpuidle in order
> >> to read some statistics from there and investigate the behavior ?
> > 
> > What exactly would you like to see in there?
> 
> It could be interesting to have statistics on a per cpu and global basis
> for:
> 
> - prediction accuracy:
> 
> /sys/kernel/debug/cpuidle/prediction/[good|over|under]
> /sys/kernel/debug/cpuidle/cpu*/state*/prediction/[good|over|under]
> 
>  - exit latency
> 
> In addition, it is often the case the idle states values are dropped
> randomly, it is interesting to see the average exit latency for the
> states. That could give also an indication the cluster idle state success.
> 
> /sys/kernel/debug/cpuidle/state*/latency/[min|max|avg|stddev]
> /sys/kernel/debug/cpuidle/cpu*/state*/prediction/[min|max|avg|stddev]
> 
> And perhaps more information like the tick stopped stat ?

Fair enough, but that must be minimum overhead.