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

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Date:	Thu, 24 Mar 2011 22:22:00 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>
Cc:	Len Brown <lenb@...nel.org>, 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

* Trinabh Gupta <trinabh@...ux.vnet.ibm.com> [2011-03-24 19:43:43]:


[snip]

> >>But we also have to replace the functionality provided by pm_idle,
> >>i.e. call default_idle for platforms where no better idle routine
> >>exists, call mwait for pre-nehalem platforms, use intel_idle or
> >>acpi_idle for nehalem architectures etc. To manage all this
> >>we need a registration mechanism which is conveniently provided
> >>by cpuidle.
> >
> >It isn't immediately clear to me that all of these options
> >need to be preserved.
> 
> So what do you suggest can be removed?

Can we use safe_halt() until intel_idle/acpi_idle take over? But what
if they do not take over?  If safe_halt() is not very bad compared to
the variants like mwait_idle and c1e_idle, then we can remove the old
code and no need to move them to default driver.

> >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.
> >
> >OTOH, if cpuidle is included, I'd like to see the
> >non-cpuidle code excluded, since nobody will run it...

The non-cpuidle code will be the select_idle_routine() and related
function that cam move to default_driver that register to cpuidle.
We can load on-demand as module if better routines fail to register.
Maybe we don't need this at all as discussed in the above point?

--Vaidy

[snip]

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