linux-kernel - Re: Bandwidth Allocations under CFQ I/O Scheduler

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Message-Id: <1161048269.3245.26.camel@laptopd505.fenrus.org>
Date:	Tue, 17 Oct 2006 03:24:29 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	"Phetteplace, Thad (GE Healthcare, consultant)" 
	<Thad.Phetteplace@...com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Bandwidth Allocations under CFQ I/O Scheduler

On Mon, 2006-10-16 at 16:46 -0400, Phetteplace, Thad (GE Healthcare,
consultant) wrote:
> The I/O priority levels available under the CFQ scheduler are
> nice (no pun in intended), but I remember some talk back when
> they first went in that future versions might include bandwidth
> allocations in addition to the 'niceness' style.  Is anyone out
> there working on that?  If not, I'm willing to hack up a proof
> of concept... I just wan't to make sure I'm not reinventing
> the wheel.


Hi,

it's a nice idea in theory. However... since IO bandwidth for seeks is
about 1% to 3% of that of sequential IO (on disks at least), which
bandwidth do you want to allocate? "worst case" you need to use the
all-seeks bandwidth, but that's so far away from "best case" that it may
well not be relevant in practice. Yet there are real world cases where
for a period of time you approach worst case behavior ;(

Greetings,
   Arjan van de Ven
-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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