linux-kernel - Re: [PATCH]PM QOS refresh against next-20100430

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Date:	Tue, 4 May 2010 06:16:37 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jonathan Corbet <corbet@....net>
Cc:	Kevin Hilman <khilman@...prootsystems.com>, mgross@...ux.intel.com,
	aili@...eaurora.org, dwalker@...eaurora.org, tiwai@...e.de,
	bruce.w.allan@...el.com, davidb@...cinc.com, mcgrof@...il.com,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]PM QOS refresh against next-20100430

On Mon 2010-05-03 10:42:50, Jonathan Corbet wrote:
> On Mon, 03 May 2010 09:40:11 -0700
> Kevin Hilman <khilman@...prootsystems.com> wrote:
> 
> > > One question, though...  one clear use of this API is for drivers to
> > > say "don't go into C3 or deeper because things go wrong"; I'm about to
> > > add another one of those.  It works, but the use of a
> > > PM_QOS_CPU_DMA_LATENCY requirement with a hard-coded number that one
> > > hopes is small enough seems a bit...indirect.  I wonder if it would be
> > > clearer and more robust to add a new requirement^Wrequest type saying
> > > "the quality of service I need is shallow sleeps only"?  
> > 
> > The problem with that is portability.
> > 
> > What does "shallow" mean?  
> 
> Well, shallow could mean that the state lacks the CPUIDLE_FLAG_DEEP
> flag; that should be relatively portable.  In any case, it seems more
> so than "if I put in a 55us latency requirement, I'll stay out of C3".

While C3 has maximum allowed latency (101usec, iirc), I believe
there's no minimum, so someone could create platform with really quick
C3 with perhaps only 10usec to enter...

								Pavel


-- 
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