linux-kernel - Re: SCSI sr driver: parallel writes to optical serialized which hurts performance (sr

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Message-ID: <20160307121342.3ecab454@lxorguk.ukuu.org.uk>
Date:	Mon, 7 Mar 2016 12:13:42 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	"Thomas Schmitt" <scdbackup@....net>
Cc:	linux-kernel@...r.kernel.org, jrdejong@...il.com
Subject: Re: SCSI sr driver: parallel writes to optical serialized which
 hurts performance (sr_mutex)

On Sat, 05 Mar 2016 21:47:00 +0100
"Thomas Schmitt" <scdbackup@....net> wrote:

> Hi,
> 
> as developer of libburn i got several user complaints about poor
> concurrent throughput. Since last year i suffer from it myself
> on kernel 3.16 of Debian 8. Before i had 2.6.18 which did very well
> in that aspect.
> 
> An old workaround for IDE master-slave concurrency problems brings
> a certain degree of relief on some drives. See
>   http://libburnia-project.org/wiki/ConcurrentLinuxSr
> 
> But the much better solution would be to remove the need for the
> global lock shared by all ioctl(SG_IO) to all /dev/sr*.
> 
> Given the old reports of Otto Meta about possible race conditions
> with drives at the same IDE controller, and the rareness of IDE
> attached drives nowadays, i propose to keep the global sr_mutex lock
> for IDE attached drives.

If there are race conditions present in the libata drivers then they want
fixing there. The old IDE drivers are basically obsoleted by libata for
all real world uses and most "IDE" devices are actually SATA now anyway.

Alan