linux-kernel - Re: [PATCH 1/2] lib: Proportions with flexible period

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Message-ID: <20120518144217.GC6875@quack.suse.cz>
Date:	Fri, 18 May 2012 16:42:17 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] lib: Proportions with flexible period

On Thu 17-05-12 23:56:45, Peter Zijlstra wrote:
> On Tue, 2012-05-15 at 17:43 +0200, Jan Kara wrote:
> > +void fprop_fraction_percpu(struct fprop_global *p,
> > +                          struct fprop_local_percpu *pl,
> > +                          unsigned long *numerator, unsigned long *denominator)
> > +{
> > +       unsigned int seq;
> > +       s64 den;
> > +
> > +       do {
> > +               seq = read_seqcount_begin(&p->sequence);
> > +               fprop_reflect_period_percpu(p, pl);
> > +               *numerator = percpu_counter_read_positive(&pl->events);
> > +               den = percpu_counter_read(&p->events);
> > +               if (den <= 0)
> > +                       den = percpu_counter_sum(&p->events);
> > +               *denominator = den;
> > +       } while (read_seqcount_retry(&p->sequence, seq));
> > +} 
> 
> 
> why not use percpu_counter_read_positive(&p->events) and ditch
> percpu_counter_sum()? That sum can be terribly expensive..
  Yes. I'm actually not sure why I used the _sum here... Thanks for
spotting this.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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