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From: Benjamin LaHaise <bcrl@kvack.org>
To: Nate Diller <nate.diller@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	Nate Diller <nate@agami.com>, Andrew Morton <akpm@osdl.org>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Trond Myklebust <trond.myklebust@fys.uio.no>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Suparna Bhattacharya <suparna@in.ibm.com>,
	Kenneth W Chen <kenneth.w.chen@intel.com>,
	David Brownell <dbrownell@users.sourceforge.net>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	netdev@vger.kernel.org, ocfs2-devel@oss.oracle.com,
	linux-aio@kvack.org, xfs-masters@oss.sgi.com
Subject: Re: [PATCH -mm 0/10][RFC] aio: make struct kiocb private
Date: Wed, 17 Jan 2007 16:52:30 -0500	[thread overview]
Message-ID: <20070117215230.GB28828@kvack.org> (raw)
In-Reply-To: <5c49b0ed0701152025t2e9fdd6cld36b077f36c78afe@mail.gmail.com>

On Mon, Jan 15, 2007 at 08:25:15PM -0800, Nate Diller wrote:
> the right thing to do from a design perspective.  Hopefully it enables
> a new architecture that can reduce context switches in I/O completion,
> and reduce overhead.  That's the real motive ;)

And it's a broken motive.  Context switches per se are not bad, as they 
make it possible to properly schedule code in a busy system (which is 
*very* important when realtime concerns come into play).  Have a look 
at how things were done in the 2.4 aio code to see how completion would 
get done with a non-retry method, typically in interrupt context.  I had 
code that did direct I/O rather differently by sharing code with the 
read/write code paths at some point, the catch being that it was pretty 
invasive, which meant that it never got merged with the changes to handle 
writeback pressure and other work that happened during 2.5.

That said, you can't make kiocb private without completely removing the 
ability of the rest of the kernel to complete an aio sanely from irq context.  
You need some form of i/o descriptor, and a kiocb is just that.  Adding more 
layering is just going to make things messier and slower for no real gain.

		-ben
-- 
"Time is of no importance, Mr. President, only life is important."
Don't Email: <dont@kvack.org>.

  parent reply	other threads:[~2007-01-17 21:52 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  1:54 Nate Diller
2007-01-16  1:54 ` [PATCH -mm 7/10][RFC] aio: make __blockdev_direct_IO use file_endio_t Nate Diller
2007-01-16  1:54 ` [PATCH -mm 4/10][RFC] aio: convert aio_complete to file_endio_t Nate Diller
2007-01-16  5:53   ` David Brownell
2007-01-16  9:21     ` Nate Diller
2007-01-16  1:54 ` [PATCH -mm 5/10][RFC] aio: make blk_directIO use file_endio_t Nate Diller
2007-01-16  1:54 ` [PATCH -mm 8/10][RFC] aio: make direct_IO aops " Nate Diller
2007-01-16  1:54 ` [PATCH -mm 1/10][RFC] aio: scm remove struct siocb Nate Diller
2007-01-16  1:54 ` [PATCH -mm 6/10][RFC] aio: make nfs_directIO use file_endio_t Nate Diller
2007-01-16  1:54 ` [PATCH -mm 10/10][RFC] aio: convert file aio to file_endio_t Nate Diller
2007-01-16  1:54 ` [PATCH -mm 2/10][RFC] aio: net use struct socket for io Nate Diller
2007-01-16  5:44   ` Stephen Hemminger
2007-01-16 10:24     ` Evgeniy Polyakov
2007-01-16  1:54 ` [PATCH -mm 9/10][RFC] aio: usb gadget remove aio file ops Nate Diller
2007-01-16  6:05   ` David Brownell
2007-01-16  9:13     ` Nate Diller
2007-01-16 18:36       ` David Brownell
2007-01-16  1:54 ` [PATCH -mm 3/10][RFC] aio: use iov_length instead of ki_left Nate Diller
2007-01-16  2:14   ` Christoph Hellwig
2007-01-16  5:37     ` Nate Diller
2007-01-16 23:36       ` Ingo Oeser
2007-01-18  4:27     ` Vectored AIO breakage for sockets and pipes ? Suparna Bhattacharya
2007-01-18 21:40       ` Zach Brown
2007-01-16  3:23 ` [PATCH -mm 0/10][RFC] aio: make struct kiocb private Christoph Hellwig
2007-01-16  4:25   ` Nate Diller
2007-01-16  8:22     ` David Brownell
2007-01-17 21:52     ` Benjamin LaHaise [this message]
2007-01-17 23:30       ` Nate Diller

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