linux-kernel - Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

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Message-ID: <20170714155853.xvoyyzjg6l2ytqx7@hirez.programming.kicks-ass.net>
Date:   Fri, 14 Jul 2017 17:58:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Aubrey Li <aubrey.li@...el.com>, tglx@...utronix.de,
        len.brown@...el.com, rjw@...ysocki.net, tim.c.chen@...ux.intel.com,
        paulmck@...ux.vnet.ibm.com, yang.zhang.wz@...il.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods

On Fri, Jul 14, 2017 at 08:52:28AM -0700, Arjan van de Ven wrote:
> On 7/14/2017 8:38 AM, Peter Zijlstra wrote:
> > No, that's wrong. We want to fix the normal C state selection process to
> > pick the right C state.
> > 
> > The fast-idle criteria could cut off a whole bunch of available C
> > states. We need to understand why our current C state pick is wrong and
> > amend the algorithm to do better. Not just bolt something on the side.
> 
> I can see a fast path through selection if you know the upper bound of any
> selection is just 1 state.
> 
> But also, how much of this is about "C1 be fast" versus "selecting C1 is slow"

I got the impression its about we need to select C1 for longer. But the
fact that the patches don't in fact answer any of these questions,
they're wrong in principle ;-)