linux-kernel - Re: splice methods in character device driver

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Message-ID: <20090616182810.GD11363@kernel.dk>
Date:	Tue, 16 Jun 2009 20:28:10 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Steve Rottinger <steve@...tek.com>
Cc:	Leon Woestenberg <leon.woestenberg@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: splice methods in character device driver

On Tue, Jun 16 2009, Steve Rottinger wrote:
> >> I'm doing about 300MB/s to my hardware RAID, running two instances of my
> >> splice() copy application
> >> (One on each RAID channel).  I would like to combine the two RAID
> >> channels using a software RAID 0;
> >> however, splice, even from /dev/zero runs horribly slow to a software
> >> RAID device.  I'd be curious
> >> to know if anyone else has tried this?
> >>     
> >
> > Did you trace it and find out why it was slow? It should not be. Moving
> > 300MB/sec should not be making any machine sweat.
> >
> I haven't dug into this too deeply, yet; however, I did discover
> something interesting: The splice runs much faster using the software
> raid, if I transfer to a file on a mounted filesystem, instead of the
> raw md block device. 

OK, that's a least a starting point. I'll try this tomorrow (raw block
device vs fs file).

-- 
Jens Axboe

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