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Date:	Sat, 17 Mar 2012 16:28:53 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Wakko Warner <wakko@...mx.eu.org>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: Burning multiple DVDs at one time

On Mar 17 Wakko Warner wrote:
> Stefan Richter wrote:
> > On Mar 15 Wakko Warner wrote:
> > > I'm having problems doing this.
> > > 
> > > When I burn a single disk, wodim shows the drive buf @ 99% consistently. 
> > > The instant that a 2nd disk is being burned, the drive buf on the first one
> > > starts to drop and data stops when the 2nd wodim is performing OPC.
> > > 
> > > During the burn of both discs, the drive buf will drop on both until one of
> > > them finishes.  Both drives see under runs.
> > > 
> > > When one starts fixating, the other will hang until the fixation is
> > > completed.
> > > 
> > > During the burns, the fifo of both never drop below 99%
> > > 
> > > There are no logs that are produced.
> > > 
> > > My burners are:
> > > [6:0:0:0]    cd/dvd  ATAPI    iHAS422   8      4L11  /dev/sr7
> > > [7:0:0:0]    cd/dvd  ATAPI    iHAS224   B      GL05  /dev/sr8
> > > 
> > > Both are SATA drives attached to the onboard sata controller
> > > 00:1f.2 SATA controller: Intel Corporation 631xESB/632xESB SATA AHCI Controller (rev 09)
> > > 00:1f.2 0106: 8086:2681 (rev 09)
[...]
> > This is likely due to serialization by a global mutex in the sr driver.
> > Have a look at thread "[PATCH] [SCSI] sr: fix multi-drive performance,
> > remove BKL replacement" from February. https://lkml.org/lkml/2012/2/28/230
> 
> Thanks.  I looked at the patch.  I would just like to confirm that I can
> patch my 3.0.0 vanilla kernel, compile the sr module, unload the current and
> load the patched one without the need to reboot.

Yes, this should be possible.

Oh, I only noticed just know that you also wrote:

> > > The kernel is a vanilla kernel v3.0.0.  (This also happened with 2.6.35)

In 2.6.35, the Big Kernel Lock was still in place there.  That lock
behaved differently from a plain mutex --- notably it was released when a
thread went to sleep --- so maybe there is more to your problem than just
sr_mutex blocking unrelated sr accesses.
-- 
Stefan Richter
-=====-===-- --== =---=
http://arcgraph.de/sr/
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