linux-kernel - Re: [PATCH 2/2] block: Convert BDI proportion calculations to flexible proportions

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Message-ID: <20120531224206.GC19050@quack.suse.cz>
Date:	Fri, 1 Jun 2012 00:42:06 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Sasha Levin <levinsasha928@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to
 flexible proportions

On Fri 01-06-12 00:26:05, Peter Zijlstra wrote:
> On Fri, 2012-06-01 at 00:11 +0200, Jan Kara wrote:
> >  bool fprop_new_period(struct fprop_global *p, int periods)
> >  {
> > -       u64 events = percpu_counter_sum(&p->events);
> > +       u64 events;
> > +       unsigned long flags;
> >  
> > +       local_irq_save(flags);
> > +       events = percpu_counter_sum(&p->events);
> > +       local_irq_restore(flags);
> >         /*
> >          * Don't do anything if there are no events.
> >          */
> > @@ -73,7 +77,9 @@ bool fprop_new_period(struct fprop_global *p, int periods)
> >         if (periods < 64)
> >                 events -= events >> periods;
> >         /* Use addition to avoid losing events happening between sum and set */
> > +       local_irq_save(flags);
> >         percpu_counter_add(&p->events, -events);
> > +       local_irq_restore(flags);
> >         p->period += periods;
> >         write_seqcount_end(&p->sequence); 
> 
> Uhm, why bother enabling it in between? Just wrap the whole function in
> a single IRQ disable.
  I wanted to have interrupts disabled for as short as possible but if you
think it doesn't matter, I'll take your advice. The result is attached.

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

View attachment "flex-proportion-irq-save.diff" of type "text/x-patch" (1164 bytes)