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Date: Thu, 8 Feb 2001 08:57:33 -0500 (EST)
From: Ben LaHaise <bcrl@redhat.com>
To: Pavel Machek <pavel@suse.cz>
cc: Linus Torvalds <torvalds@transmeta.com>,
        Marcelo Tosatti <marcelo@conectiva.com.br>, Jens Axboe <axboe@suse.de>,
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        Linux Kernel List <linux-kernel@vger.kernel.org>,
        <kiobuf-io-devel@lists.sourceforge.net>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: select() returning busy for regular files [was Re: [Kiobuf-io-devel]
 RFC: Kernel mechanism: Compound event wait]
In-Reply-To: <20010208001735.C189@bug.ucw.cz>
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On Thu, 8 Feb 2001, Pavel Machek wrote:

> Hi!
>
> > > Its arguing against making a smart application block on the disk while its
> > > able to use the CPU for other work.
> >
> > There are currently no other alternatives in user space. You'd have to
> > create whole new interfaces for aio_read/write, and ways for the kernel to
> > inform user space that "now you can re-try submitting your IO".
>
> Why is current select() interface not good enough?

Think of random disk io scattered across the disk.  Think about aio_write
providing a means to perform zero copy io without needing to resort to
playing mm tricks write protecting pages in the user's page tables.  It's
also a means for dealing efficiently with thousands of outstanding
requests for network io.  Using a select based interface is going to be an
ugly kludge that still has all the overhead of select/poll.

		-ben

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