linux-kernel - Re: disk IO directly from PCI memory to block device sectors

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Message-ID: <20080926110610.17603d30@lxorguk.ukuu.org.uk>
Date:	Fri, 26 Sep 2008 11:06:10 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	marty <martyleisner@...oo.com>, linux-kernel@...r.kernel.org,
	martin.leisner@...ox.com
Subject: Re: disk IO directly from PCI memory to block device sectors

On Fri, 26 Sep 2008 11:11:35 +0200
Jens Axboe <jens.axboe@...cle.com> wrote:

> On Fri, Sep 26 2008, Alan Cox wrote:
> > > What I'm looking is for a more generic/driver independent way of sticking
> > > contents of PCI ram onto a disk.
> > 
> > Ermm seriously why not have a userspace task with the PCI RAM mmapped
> > and just use write() like normal sane people do ?
> 
> To avoid the fault and copy, I would assume.

It's a write to a raw partition so with O_DIRECT you won't have to copy
and MAP_POPULATE will premap the object if even the first write wants to
occur without faulting overhead.

Alan
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