linux-kernel - Re: [PATCH 2/2] UBIFS: start using hrtimers

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Date:	Fri, 29 May 2009 15:32:37 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-fsdevel@...r.kernel.org,
	Steven Rostedt <srostedt@...hat.com>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 2/2] UBIFS: start using hrtimers

On Fri, 2009-05-29 at 18:09 +0300, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
> Subject: [PATCH 2/2] UBIFS: start using hrtimers
> 
> UBIFS uses timers for write-buffer write-back. It is not
> crucial for us to write-back exactly on time. We are fine
> to write-back a little earlier or later. And this means
> we may optimize UBIFS timer so that it could be groped
> with a close timer event, so that the CPU would not be
> waken up just to do the write back. This is optimization
> to lessen power consumption, which is important in
> embedded devices UBIFS is used for.
> 
> hrtimers have a nice feature: they are effectively range
> timers, and we may defind the soft and hard limits for
> it. Standard timers do not have these feature. They may
> only be made deferrable, but this means there is effectively
> no hard limit. So, we will better use hrtimers.
> 
> Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
> ---

Seems sane enough from a hrtimer POV, but isn't this already
functionality that the VFS/pdflush provide?

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