linux-kernel - Re: [PATCH] intel-pstate: Update frequencies of policy->cpus only from ->set

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Date:	Mon, 22 Feb 2016 16:57:14 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Chen, Yu C" <yu.c.chen@...el.com>
Cc:	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH] intel-pstate: Update frequencies of policy->cpus only
 from ->set_policy()

Hi,

I am not really an intel-pstate driver guy, just wrote the patch based
on software-review of the stuff :)

On 22-02-16, 10:17, Chen, Yu C wrote:
> IIRC,
> 1.HWP is  hardwarely per-package, CPUs inside one package have one shared HWP.
> 2.Currently all the CPUs share the same HWP settings according to intel_pstate design.
> 3.  The policy is per-cpu in intel_pstate driver.(policy->cpus only contains one cpu)
> 
> So with this patch applied,  it is likely CPUs may have different HWP settings?

I think the hardware should be able to cope with that, and should be
selecting the frequency based on the highest frequency requested for
the same package. Otherwise, why should there be an option to supply
per-cpu settings ?

> For example:
> CPU 0 belongs to package A with policy 0, and CPU 1 belongs to package B with policy 1,
> If you change the policy 0 from powersave to performance, then only CPU0 will update its
> min/max freq in HWP, however we should also update CPU 2's min/max in HWP settings?
> Plz correct me  if I'm wrong..

I will let the official intel-pstate guys reply to that.

-- 
viresh