linux-kernel - Re: [PATCH 0/3] bdi write bandwidth estimation

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Message-Id: <20110613152330.056e2eba.akpm@linux-foundation.org>
Date:	Mon, 13 Jun 2011 15:23:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	<linux-fsdevel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] bdi write bandwidth estimation

On Sun, 12 Jun 2011 23:18:21 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> Do bdi write bandwidth estimation in the flusher thread at 200ms intervals,

stdrant: anything which is paced using "seconds" is basically always
wrong.  The bandwidth of storage systems varies by who-knows-how-many
orders of magnitude.  If 200ms is correct for one system then it is
vastly incorrect for another.

A more suitable clock for this estimate would be "per 200 requests",
for a block-based BDI.

Also of course the bandwidth of a particular BDI varies vastly
depending on workload.  For the purpose of this work, that's probably
a desirable thing.

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