linux-kernel - Re: [PATCH] processor passthru - upload _Cx and

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Date:	Mon, 27 Feb 2012 08:19:24 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	<ke.yu@...el.com>, <kevin.tian@...el.com>, <lenb@...nel.org>,
	<xen-devel@...ts.xensource.com>, <davej@...hat.com>,
	<cpufreq@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] processor passthru - upload _Cx and _Pxx data to
 hypervisor (v5).

>>> On 25.02.12 at 01:21, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> But cpufreq != cpuidle != cpufreq governor, and they all are run by 
> different rules.
> The ondemand cpufreq governor for example runs a timer and calls the 
> appropiate cpufreq
> driver. So with these patches I posted we end up with a cpufreq driver in 
> the kernel
> and in Xen hypervisor - both of them trying to change Pstates. Not good (to 
> be fair,
> if powernow-k8/acpi-cpufreq would try it via WRMSR -  those would up being 
> trapped and
> ignored by the hypervisor. I am not sure about the outw though).

I'm not aware of any trapping that would be done on the I/O port here;
it could be added, though (i.e. the ports removed from the list of
allowed ports of Dom0 once they become known to the hypervisor).

> The pre-RFC version of this posted driver implemented a cpufreq governor that 
> was
> nop and for future work was going to make a hypercall to get the true 
> cpufreq value
> to report properly in /proc/cpuinfo - but I hadn't figured out a way to make 
> it be
> the default one dynamically.
> 
> Perhaps having xencommons do 
> echo "xen" > /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
> 
> And s/processor-passthru/cpufreq-xen/ would do it? That would eliminate the 
> [performance,
> ondemand,powersave,etc] cpufreq governors from calling into the cpufreq 
> drivers to alter P-states.

Except that you want this to be a cpufreq driver, not a governor.

Jan

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