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

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Date:	Fri, 01 Jun 2012 00:26:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	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, 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.
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