linux-kernel - Re: [RFC PATCH V4 2/5] cpuidle: list based cpuidle driver registration and selection

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Date:	Fri, 25 Mar 2011 03:05:36 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>
Cc:	arjan@...ux.intel.com, peterz@...radead.org,
	suresh.b.siddha@...el.com, benh@...nel.crashing.org,
	venki@...gle.com, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	sfr@...b.auug.org.au, xen-devel@...ts.xensource.com
Subject: Re: [RFC PATCH V4 2/5] cpuidle: list based cpuidle driver registration
 and selection

> I think there are other problems too, related to saving and restoring
> of pm_idle pointer. For example, cpuidle itself saves current value
> of pm_idle, flips it and then restores the saved value. There is
> no guarantee that the saved function still exists. APM does exact
> same thing (though it may not be used these days).
> 
> The problem also is that a number of architectures have copied the
> same design based on pm_idle; so its spreading.

pm_idle is a primitive design yes, but I think the issue
with pm_idle is a theoretical one, at least on x86;
as there isn't any other code scribbling on pm_idle
in practice.  So this is clean-up, rather than bug-fix work...

> > It isn't immediately clear to me that all of these options
> > need to be preserved.
> 
> So what do you suggest can be removed?

I sent a series of small patches yesterday to get the ball rolling...
https://lkml.org/lkml/2011/3/24/54

I think the xen thing can go away.

I proposed that APM be removed entirely,
but that will take a few releases to conclude....

> > Are we suggesting that x86 must always build with cpuidle?
> > I'm sure that somebody someplace will object to that.
> 
> Arjan argued that since almost everyone today runs cpuidle
> it may be best to include it in the kernel
> (https://lkml.org/lkml/2010/10/20/243). But yes, we agreed
> that we would have to make cpuidle lighter incrementally.
> Making ladder governor optional could be one way for example.

ladder is already optional.

cheers,
-Len Brown, Intel Open Source Technology Center
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