linux-kernel - Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20160317094046.GF18212@e106622-lin>
Date:	Thu, 17 Mar 2016 09:40:46 +0000
From:	Juri Lelli <Juri.Lelli@....com>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Michael Turquette <mturquette@...libre.com>, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	morten.rasmussen@....com, dietmar.eggemann@....com,
	vincent.guittot@...aro.org,
	Michael Turquette <mturquette+renesas@...libre.com>,
	Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 16/03/16 10:55, Steve Muckle wrote:
> On 03/16/2016 03:02 AM, Juri Lelli wrote:
> > Hi,
> > 
> > On 16/03/16 09:05, Peter Zijlstra wrote:
> >> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> >>>> Then again, maybe this knob will be part of the mythical
> >>>> power-vs-performance slider?
> >>>
> >>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> >>> mythical slider) aims to provide a more sophisticated interface for
> >>> tuning scheduler-driven frequency selection. In addition to a global
> >>> boost value it includes a cgroup controller as well for per-task tuning.
> >>>
> >>> I would definitely expect the margin/boost value to be modified at
> >>> runtime, for example if the battery is running low, or the user wants
> >>> 100% performance for a while, or the userspace framework wants to
> >>> temporarily tailor the performance level for a particular set of tasks, etc.
> >>
> >> OK, so how about we start with it as a debug knob, and once we have
> >> experience and feel like it is indeed a useful runtime knob, we upgrade
> >> it to ABI.
> >>
> > 
> > I tend to agree here. To me the margin is something that we need to make
> > this thing work and to get acceptable performance out of the box. So we
> > can play with it while debugging, but I consider the schedtune slider as
> > the way to tune the system at runtime.
> 
> Could the default schedtune value not serve as the out of the box margin?
> 

I'm not sure I understand you here. For me schedtune should be disabled
by default, so I'd say that it doesn't introduce any additional margin
by default. But we still need a margin to make the governor work without
schedtune in the mix.

> Regardless I agree that a debug interface is the way to go for now while
> we figure things out.
> 

Looks good to me.

Best,

- Juri