linux-kernel - RE: async I/O seems to be blocking on 2.6.15

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Message-ID: <Pine.LNX.4.64.0611061903220.27775@debian.freesoft.org>
Date:	Mon, 6 Nov 2006 19:03:59 -0500 (EST)
From:	Brent Baccala <cosine@...esoft.org>
To:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
cc:	linux-kernel@...r.kernel.org
Subject: RE: async I/O seems to be blocking on 2.6.15

On Mon, 6 Nov 2006, Chen, Kenneth W wrote:

> I've tried that myself too and see similar result.  One thing to note is
> that I/O being submitted are pretty big at 1MB, so the vector list inside
> bio is going to be pretty long and it will take a while to construct that.
> Drop the size for each I/O to something like 4KB will significantly reduce
> the time.  I haven't done the measurement whether the time to submit I/O
> grows linearly with respect to I/O size.  Most likely it will.  If it is
> not, then we might have a scaling problem (though I don't believe we have
> this problem).
> 
> - Ken
> 
>

I'm basically an end user here (as far as the kernel is concerned), so
let me ask the basic "dumb user" question here:

How should I do my async I/O if I just want to read or write
sequentially through a file, using O_DIRECT, and letting the CPU get
some work done in the meantime?  What about more random access?

I've already concluded that I should try to keep my read and write
files on seperate disks and hopefully on seperate controllers, but I
still seem to be fighting this thing to keep it from blocking.

 					-bwb

 					Brent Baccala
 					cosine@...esoft.org
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