linux-kernel - Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

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: <acd9c300-8be6-e87b-5583-191fd5bda94c@arm.com>
Date:   Thu, 13 Jul 2017 14:08:13 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Sudeep Holla <sudeep.holla@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Juri Lelli <juri.lelli@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant
 load-tracking support

On 13/07/17 13:40, Sudeep Holla wrote:
> 
> 
> On 11/07/17 16:21, Dietmar Eggemann wrote:
>> On 11/07/17 07:39, Viresh Kumar wrote:
>>> On 10-07-17, 14:46, Rafael J. Wysocki wrote:

[...]

>> Like I said in the other email, since for (future)
>> arm/arm64 fast-switch driver, the return value of
>> cpufreq_driver->fast_switch() does not give us the information that the
>> frequency value did actually change, we have to implement
> 
> I was under the impression that we strictly don't care about that
> information when I started exploring the fast_switch with the standard
> firmware interface on ARM platforms(until if and when ARM provides an
> instruction to achieve that).
> 
> If f/w failed to change the frequency, will that be not corrected in the
> next sample or instance. I would like to know the impact of absence of
> such notifications.

In the meantime we agreed that we have to invoke frequency invariance
from within the cpufreq driver.

For a fast-switch driver I would have to put the call to
arch_set_freq_scale() somewhere where I know that the frequency has been
set.

Without a notification (from the firmware) that the frequency has been
set, I would have to call arch_set_freq_scale() somewhere in the
driver::fast_switch() call assuming that the frequency has been actually
set.

[...]