linux-kernel - Re: O_DIRECT question

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Date:	Thu, 25 Jan 2007 22:11:38 +0100
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Phillip Susi <psusi@....rr.com>,
	Linus Torvalds <torvalds@...l.org>, Viktor <vvp01@...ox.ru>,
	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@in
Subject: Re: O_DIRECT question

On Thursday 25 January 2007 21:45, Michael Tokarev wrote:
> Phillip Susi wrote:
> > Denis Vlasenko wrote:
> >> You mean "You can use aio_write" ?
> > 
> > Exactly.  You generally don't use O_DIRECT without aio.  Combining the
> > two is what gives the big win.
> 
> Well, it's not only aio.  Multithreaded I/O also helps alot -- all this,
> say, to utilize a raid array with many spindles.
> 
> But even single-threaded I/O but in large quantities benefits from O_DIRECT
> significantly, and I pointed this out before.

Which shouldn't be true. There is no fundamental reason why
ordinary writes should be slower than O_DIRECT.
--
vda
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