linux-kernel - Re: [PATCH 3/3] sched: Optimize !CONFIG_NO_HZ

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Message-ID: <20160408174414.GE1087@worktop>
Date:	Fri, 8 Apr 2016 19:44:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Byungchul Park <byungchul.park@....com>,
	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>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 3/3] sched: Optimize !CONFIG_NO_HZ_COMMON cpu load updates

On Fri, Apr 08, 2016 at 02:55:22PM +0200, Frederic Weisbecker wrote:
> > > @@ -4540,17 +4568,8 @@ static void cpu_load_update(struct rq *this_rq, unsigned long this_load,
> > >  
> > >  		/* scale is effectively 1 << i now, and >> i divides by scale */
> > >  
> > > -		old_load = this_rq->cpu_load[i];
> > #ifdef CONFIG_NO_HZ_COMMON
> > > -		old_load = decay_load_missed(old_load, pending_updates - 1, i);
> > > -		if (tickless_load) {
> > > -			old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
> > > -			/*
> > > -			 * old_load can never be a negative value because a
> > > -			 * decayed tickless_load cannot be greater than the
> > > -			 * original tickless_load.
> > > -			 */
> > > -			old_load += tickless_load;
> > > -		}
> > #endif
> 
> Ah sure, if you prefer it that way, I can do that.

Yes please. I normally favour the thing you did, but here it makes
tricky code that much harder to read.