linux-kernel - Re: [PATCH 1/3] cpuidle: If disable_cpuidle() is called, set pm_idle to default

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Date:	Wed, 9 Nov 2011 09:44:41 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org, len.brown@...el.com,
	tglx@...utronix.de, jeremy@...p.org, hpa@...or.com, bp@...en8.de,
	tj@...nel.org, trenn@...e.de, mingo@...hat.com,
	xen-devel@...ts.xensource.com, stable@...nel.org
Subject: Re: [PATCH 1/3] cpuidle: If disable_cpuidle() is called, set pm_idle
 to default_idle.

. snip..
> > 
> >      ..scribble on pm_idle and access default_idle,
> >     have it simply disable_cpuidle() so acpi_idle will not load and
> >     architecture default HLT will be used.
> > 
> > .. but the default HLT does not get used. Instead we end up in the

Hey Deepthi,

> > +	if (cpuidle_disabled()) {
> > +		pm_idle = default_idle;
> > +		return;
> > +	}
> 
> 
> The above check is needed to initialise pm_idle to default_idle if
> cpuidle is disabled but this requirement here is Zen specific. 
> On other architectures, if cpuidle is disabled on boot then we 
> rather would want mwait_idle or amd_e400_idle to be enabled than 
> default_idle. Can we make this check Zen specific ? 

We do? Why? I would have thought that if you want to disable the cpuidle
you would want the default_idle. 

Perhaps there is another way do this is:

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index becd6d9..04b10a4 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -38,6 +38,7 @@ int cpuidle_disabled(void)
 void disable_cpuidle(void)
 {
 	off = 1;
+	pm_idle = default_idle;
 }

which would do almost the same thing as this patch (well, except
that if you run cpuidle.off=1 you still end up with amd_e400_idle
instead of default_idle, so it is not the complete solution).

> 
> ...  if(ZEN_ARCH && cpuidle_disabled()) ... 

That would not work very well. For one thing you would need to call
'xen_domain()', and pull in a lots of header files. Second of, it
looks quite ugly and kernel folks like pretty code.
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