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From: Denis Vlasenko <vda.linux@googlemail.com>
To: Michael Tokarev <mjt@tls.msk.ru>
Subject: Re: O_DIRECT question
Date: Thu, 25 Jan 2007 22:11:38 +0100
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Cc: Phillip Susi <psusi@cfl.rr.com>, Linus Torvalds <torvalds@osdl.org>,
       Viktor <vvp01@inbox.ru>, Aubrey <aubreylee@gmail.com>,
       Hua Zhong <hzhong@gmail.com>, Hugh Dickins <hugh@veritas.com>,
       linux-kernel@vger.kernel.org, hch@infradead.org, kenneth.w.chen@in
References: <6d6a94c50701101857v2af1e097xde69e592135e54ae@mail.gmail.com> <45B90D19.60106@cfl.rr.com> <45B916F2.4070906@tls.msk.ru>
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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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