linux-kernel - Re: O_DIRECT question

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Message-ID:  <mj+md-20070111.130016.22349.camellia@ucw.cz>
Date:	Thu, 11 Jan 2007 14:06:54 +0100
From:	Martin Mares <mj@....cz>
To:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
Cc:	Aubrey <aubreylee@...il.com>, Hua Zhong <hzhong@...il.com>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	hch@...radead.org, kenneth.w.chen@...el.com, akpm@...l.org,
	torvalds@...l.org, mjt@....msk.ru
Subject: Re: O_DIRECT question

Hello!

> Maybe you need to say why you want to use O_DIRECT with its terrible
> performance?

Incidentally, I was writing an external-memory radix-sort some time ago
and it turned out that writing to 256 files at once is much faster with
O_DIRECT than through the page cache, very likely because the page cache
is flushing pages in essentially random order. Tweaking VM parameters
and block device queue size helped, but only a little.

				Have a nice fortnight
-- 
Martin `MJ' Mares                          <mj@....cz>   http://mj.ucw.cz/
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
Linux vs. Windows is a no-WIN situation.
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