linux-kernel - Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection

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Message-ID: <20151110104159.022758a3@icelake>
Date:	Tue, 10 Nov 2015 10:41:59 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Andi Kleen <andi.kleen@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Eduardo Valentin <edubezval@...il.com>,
	Punit Agrawal <punit.agrawal@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC PATCH v2 3/3] sched: introduce synchronized idle injection

On Tue, 10 Nov 2015 14:23:24 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> > +/* protect injection parameters from runtime changes */
> > +static DEFINE_SPINLOCK(idle_inject_lock);  
> 
> A global lock, yay :-), I think you want this to be a RAW_SPINLOCK
> though. As on -RT this would want to actually run from IRQ context
> too.
> 
I am not using this lock in per cpu timer handler, I guess it would not
be in IRQ context?
> > +	if (bitmap_weight(idle_inject_cpumask,
> > num_possible_cpus())) {  
> 
> I don't get the point of this bitmap; with the cpu notifier you
> basically ensure this is equal to online_mask.
> 
> Also, this weight test is pointless, if the bitmap is empty the
> for_each_set_bit() should be of equal cost -- and afaict nothing
> calling this is performance critical in the first place.
Agreed, I will remove that. I was planning on a subset of CPUs but not
for now, e.g. a socket or domain.
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