linux-kernel - Re: Rich man's version of AIO on Linux 2.6.x?

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Message-ID: <20090522145457.GC7234@tiehlicka.suse.cz>
Date:	Fri, 22 May 2009 16:54:58 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Leon Woestenberg <leon.woestenberg@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	devel@...uxdriverproject.org
Subject: Re: Rich man's version of AIO on Linux 2.6.x?

On Fri 22-05-09 02:59:53, Leon Woestenberg wrote:
> Hello,

Hi

> 
> On the state-of-art of asynchronous I/O in Linux. I understand we have
> full support for AIO in the Linux 2.6.x kernel but I cannot find how
> to use it from user space.
> 
> 
> I would like to exploit AIO in hardware and the device driver for it,
> by keeping the hardware performing I/O at all times (no setup latency
> between requests by allowing multiple
> I/O requests to be queued in hardware). Note this is a character
> device, not a filesystem.
> 
> I implemented aio_read() and aio_write() on my character device
> interface, but it's never been called; read() and write() is called
> instead.
> 
> From "Understanding the Linux kernel, 3rd edition" I read that glibc
> indeed implements aio_read() and friends itself, not through the
> kernel AIO syscalls.
> 
> <Quote>
> Essentially, the aio_read( ) or aio_write( ) library function clones
> the current process and lets the child invoke the synchronous read( )
> or write( ) system calls; However, this "poor man's" version of the
> POSIX functions is significantly slower than a version that uses a
> kernel-level implementation of asynchronous I/O.
> <End Quote>
> 
> I am looking for a rich man's way to use the kernel functionality;
> essentially I want my drivers aio_read and aio_write ops to be called.

Check the libaio library (io_submit and friends)

> 
> Regards,
> -- 
> Leon
> --
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-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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