linux-kernel - Re: O_DIRECT question

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Message-ID: <45A7F4F2.2080903@tls.msk.ru>
Date:	Fri, 12 Jan 2007 23:52:02 +0300
From:	Michael Tokarev <mjt@....msk.ru>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	Chris Mason <chris.mason@...cle.com>,
	Linus Torvalds <torvalds@...l.org>,
	dean gaudet <dean@...tic.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@...el.com, akpm@...l.org
Subject: Re: O_DIRECT question

Michael Tokarev wrote:
[]
> After all the explanations, I still don't see anything wrong with the
> interface itself.  O_DIRECT isn't "different semantics" - we're still
> writing and reading some data.  Yes, O_DIRECT and non-O_DIRECT usages
> somewhat contradicts with each other, but there are other ways to make
> the two happy, instead of introducing alot of stupid, complex, and racy
> code all over.

By the way.  I just ran - for fun - a read test of a raid array.

Reading blocks of size 512kbytes, starting at random places on a 400Gb
array, doing 64threads.

 O_DIRECT: 336.73 MB/sec.
!O_DIRECT: 146.00 MB/sec.

Quite a... difference here.

Using posix_fadvice() does not improve it.

/mjt
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