linux-kernel - Re: O_DIRECT question

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Date:	Sat, 20 Jan 2007 17:36:22 +0100
From:	Denis Vlasenko <vda.linux@...glemail.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	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@...el.com, akpm@...l.org
Subject: Re: O_DIRECT question

On Thursday 11 January 2007 18:13, Michael Tokarev wrote:
> example, which isn't quite possible now from userspace.  But as long as
> O_DIRECT actually writes data before returning from write() call (as it
> seems to be the case at least with a normal filesystem on a real block
> device - I don't touch corner cases like nfs here), it's pretty much
> THE ideal solution, at least from the application (developer) standpoint.

Why do you want to wait while 100 megs of data are being written?
You _have to_ have threaded db code in order to not waste
gobs of CPU time on UP + even with that you eat context switch
penalty anyway.

I hope you agree that threaded code is not ideal performance-wise
- async IO is better. O_DIRECT is strictly sync IO.
--
vda
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