linux-kernel - Re: [PATCH 2/4] sched: Consolidate nohz CPU load update code

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Message-ID: <20160119164933.GB5317@lerouge>
Date:	Tue, 19 Jan 2016 17:49:34 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Byungchul Park <byungchul.park@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/4] sched: Consolidate nohz CPU load update code

On Thu, Jan 14, 2016 at 02:18:40PM +0900, Byungchul Park wrote:
> On Wed, Jan 13, 2016 at 05:01:29PM +0100, Frederic Weisbecker wrote:
> >  #ifdef CONFIG_NO_HZ_COMMON
> > +static void __update_cpu_load_nohz(struct rq *this_rq,
> > +				   unsigned long curr_jiffies,
> 
> Do we need to pass current jiffies as a function parameter?

I guess we don't, I just wasn't much sure of the possible overhead of READ_ONCE()

> 
> > +				   unsigned long load,
> > +				   int active)
> > +{
> > +	unsigned long pending_updates;
> > +
> > +	pending_updates = curr_jiffies - this_rq->last_load_update_tick;
> > +	if (pending_updates) {
> > +		this_rq->last_load_update_tick = curr_jiffies;
> > +		/*
> > +		 * In the regular NOHZ case, we were idle, this means load 0.
> > +		 * In the NOHZ_FULL case, we were non-idle, we should consider
> > +		 * its weighted load.
> > +		 */
> > +		__update_cpu_load(this_rq, load, pending_updates, active);
> > +	}
> > +}