linux-kernel - Re: [PATCH v3] powercap/rapl: reduce ipi calls

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Date:	Wed, 17 Feb 2016 10:04:04 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3] powercap/rapl: reduce ipi calls

On Wed, 17 Feb 2016 17:04:41 +0100 (CET)
Thomas Gleixner <tglx@...utronix.de> wrote:

> > >  
> > >  	for_each_online_cpu(i) {
> > >  		if (topology_physical_package_id(i) ==
> > > package_id)  
> 
> This is still crap. We really want a proper handling for that which
> does not require these silly for_each_cpu() loops.
> 
> That code already has a hotplug notifier, so you can track one online
> cpu in the package like we do in cqm and other facilities.
> 
> The first online cpu of a package sets itself as 'owner'. On unplug
> it looks up:
> 
> 	rpl->cpu = cpumask_any_but(topology_core_cpumask(cpu), cpu);
> 
> So if this is the last cpu then rpl->cpu becomes nr_cpu_ids.
> 
> So that whole nonsense can be avoided completely.
ok, that would work nicely, similar to cqm_pick_event_reader().
thanks for the tip. just fyi, unlike perf cqm, rapl runtime change is
expected to be low frequency.