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Message-ID: <45BA4720.5010406@tmr.com>
Date:	Fri, 26 Jan 2007 13:23:28 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Denis Vlasenko <vda.linux@...glemail.com>
CC:	Michael Tokarev <mjt@....msk.ru>, 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

Denis Vlasenko wrote:
> 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.
> 
Other than the copy to buffer taking CPU and memory resources.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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