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Message-ID: <1337351677.573.44.camel@twins>
Subject: Re: [PATCH 2/2] block: Convert BDI proportion calculations to
 flexible proportions
From: Peter Zijlstra <peterz@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>, LKML <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org
Date: Fri, 18 May 2012 16:34:37 +0200
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On Fri, 2012-05-18 at 16:24 +0200, Jan Kara wrote:
>   Yeah, that should be easy enough so I'll try it that way since I presume
> it's nicer to power usage to use deferred timers if it's reasonably
> possible. 

Btw, your current scheme also drifts. Since you do jiffes + 3*HZ you
period might actually be longer if the timer got delayed.

If you keep an external jiffies count like:

unsigned long period_jiffies = jiffies;

void my_timer_func()
{
	unsigned long delta = jiffies - period_jiffies;
	unsigned long periods = delta / 3*HZ;

	age(periods);

	period_jiffies += 3*HZ * periods;
	mod_timer(&my_timer, period_jiffies);
}


it all works without drift (+- bugs of course).