linux-kernel - Re: cpuidle and cpufreq coupling?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJZ5v0i2B0=cPB5VxXJUb36LW9hp_L7k-moj+Eg+vPvfPHFcSA@mail.gmail.com>
Date:   Thu, 20 Jul 2017 01:17:28 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Markus Mayer <code@...yer.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: cpuidle and cpufreq coupling?

On Thu, Jul 20, 2017 at 12:54 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
> Hi,
>
> We have a particular ARM CPU design that is drawing quite a lot of
> current upon exit from WFI, and it does so in a way even before the
> first instruction out of WFI is executed. That means we cannot influence
> directly the exit from WFI other than by changing the state in which it
> would be previously entered because of this "dead" time during which the
> internal logic needs to ramp up back where it left.
>
> A naive approach to solving this problem because we have CPU frequency
> scaling available would be to do the following:
>
> - just before entering WFI, switch to a low frequency OPP
> - enter WFI
> - upon exit from WFI, ramp up the frequency back to e.g: highest OPP
>
> Some of the parts that I am not exactly clear on would be:
>
> - would that qualify as a cpuidle governor of some kind that ties in
> which cpufreq?
> - would using cpufreq_driver_fast_switch() be an appropriate API to use
> from outside

Generally, the idle driver is expected to manipulate OPPs as suitable
for it at the low level.

Thanks,
Rafael