Date: Thu, 9 Feb 2012 08:51:06 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Jones <davej@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Anton Vorontsov <anton.vorontsov@linaro.org>,
        Russell King <linux@arm.linux.org.uk>, Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Nicolas Pitre <nico@fluxnic.net>, Mike Chan <mike@android.com>,
        Todd Poynor <toddpoynor@google.com>, cpufreq@vger.kernel.org,
        kernel-team@android.com, linaro-kernel@lists.linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Arjan Van De Ven <arjan@infradead.org>
Subject: Re: [PATCH RFC 0/4] Scheduler idle notifiers and users
Message-ID: <20120209075106.GB18387@elte.hu>
References: <20120208013959.GA24535@panacea>
 <1328670355.2482.68.camel@laptop>
 <20120208202314.GA28290@redhat.com>
 <1328736834.2903.33.camel@pasglop>
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* Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Wed, 2012-02-08 at 15:23 -0500, Dave Jones wrote:
> > I think the biggest mistake we ever made with cpufreq was making it
> > so configurable. If we redesign it, just say no to plugin governors,
> > and
> > yes to a lot fewer sysfs knobs.
> > 
> > So, provide mechanism to kill off all the governors, and there's a
> > migration path from what we have now to something that just works
> > in a lot more cases, while remaining configurable enough for the
> > corner-cases.
> 
> On the other hand, the need for schedulable contxts may not 
> necessarily go away.

We will support it, but the *sane* hw solution is where 
frequency transitions can be done atomically. Most workloads 
change their characteristics very quickly, and so does their 
power management profile change.

The user-space driven policy model failed for that reason: it 
was *way* too slow in reacting) - and slow hardware transitions 
suck for a similar reason as well.

We accomodate all hardware as well as we can, but we *design* 
for proper hardware. So Peter is right, this should be done 
properly.

Thanks,

	Ingo
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