linux-kernel - Re: [PATCH v2 1/3] cpufreq: add resolve

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: <20160531053011.GD9463@vireshk-i7>
Date:	Tue, 31 May 2016 11:00:11 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH v2 1/3] cpufreq: add resolve_freq driver callback

On 30-05-16, 08:31, Steve Muckle wrote:
> My goal here was to have the system operate in this case in a manner
> that is obviously not optimized (running at fmax), so the platform owner
> realizes that the cpufreq driver doesn't fully support the schedutil
> governor.
> 
> I was originally going to just return an error code but that also means
> having to check for it which would be nice to avoid if possible on this
> fast path.

Okay, I get what you are saying.

But all we are doing here is to make things fast by not sending IPIs,
etc. That should *not* lead to a behavior where the frequency stays at
MAX all the time even if the driver doesn't provide this callback or
the freq-table.

If we just return the target_freq in this case instead of UINT_MAX,
the platform may eventually have some unnecessary IPIs, wakeups, etc,
but its frequency will still be switched properly.

Wouldn't that be a better choice ?

-- 
viresh