linux-kernel - Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm

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Message-ID: <20110325180156.GC19214@dirshya.in.ibm.com>
Date:	Fri, 25 Mar 2011 23:31:57 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Len Brown <lenb@...nel.org>
Cc:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>, arjan@...ux.intel.com,
	Stephen Rothwell <sfr@...b.auug.org.au>, peterz@...radead.org,
	suresh.b.siddha@...el.com, benh@...nel.crashing.org,
	venki@...gle.com, ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xensource.com
Subject: Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm

* Len Brown <lenb@...nel.org> [2011-03-25 03:24:24]:

> 
> > Maybe there is some other way to handle asymmetry ??
> 
> When somebody invents a system that needs asymmetry on purpose,
> that is the time to get fancy.  Until that day, simply print a
> FW_BUG WARNING and fall back to default_idle().

We may print a warning but not switch to default_idle().  There could
be laptops that gets an extra C-State when run on battery.  So when
the ACPI _PPC event happens for the C-State change, we need to handle
the situation such that the states are refreshed for all CPUs in one step.

Basically while we are updating the new C-State, the framework should
not detect this as asymmetric and switch to default_idle().  Please
fell free to suggest a more elegant solution to handle the runtime
C-State change event, though symmetric across all CPUs.

--Vaidy

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