scsi/sr - Impossible to write CDs/DVDs simultaneously (since BKLremoval ?)

From: Etienne DADA
Date: Sat Oct 29 2011 - 20:11:23 EST

When burning multiple CDs/DVDs in parallel with multiple SATA drives, you can notice that :
- the process is abnormaly slow using cdrskin or wodim (top shows lots of I/O wait),
- the discs are burnt one after each other using cdrecord.

A simpler way to touch the problem is running :
$ eject /dev/sr0 & eject /dev/sr1
drives ejects sequentialy, rather than simultaneously as we were used to.

I think this problem arose after the Big Kernel Lock removal.
As far as I can understand the new "sr_mutex" private mutex in drivers/scsi/sr.c generates a per-driver locking, where a per-device locking would have been far better. I also think other drivers like sg are impacted by the same problem.

I am absolutely unable to arrange this, and would be pleased if someone competent could work on this.

Please CC me when answering as I'm not subscribing to the list.

Ãtienne DADA
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