linux-kernel - Re: [PATCH 3/9] writeback: bdi write bandwidth estimation

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Date:	Sat, 23 Jul 2011 16:07:21 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/9] writeback: bdi write bandwidth estimation

On Sat, Jul 02, 2011 at 03:29:15AM +0800, Vivek Goyal wrote:
> On Wed, Jun 29, 2011 at 10:52:48PM +0800, Wu Fengguang wrote:
> > The estimation value will start from 100MB/s and adapt to the real
> > bandwidth in seconds.
> > 
> > It tries to update the bandwidth only when disk is fully utilized.
> > Any inactive period of more than one second will be skipped.
> 
> Is this piece of code being tested in your graphs? Are there any
> inactive periods which get filtered out in your workload? I am 
> assuming in a continuous dd, we will not have periods of inactivity
> 1 second long.

There are no inactive periods in the dd tests. However I did try
"watch cat /debug/bdi/8:0/stats" while starting some write workloads
in background. When the write stops, the bandwidth does stop updating.

Thanks,
Fengguang
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