svn commit: r251372 - in stable/9/sys/cam: ata scsi

[Steven Hartland]

----- Original Message ----- 
From: "Justin T. Gibbs" <gibbs at scsiguy.com>


On Jun 4, 2013, at 3:47, Steven Hartland <smh at FreeBSD.org> wrote:

> > Author: smh
> > Date: Tue Jun  4 10:47:44 2013
> > New Revision: 251372
> > URL: http://svnweb.freebsd.org/changeset/base/251372
> > 
> > Log:
> >  Enhanced BIO_DELETE support for CAM SCSI to add ATA_TRIM support.
> > 
> >  Disable CAM BIO queue sorting for non-rotating media by default.
>
> Using the elevator makes perfect sense even for random access devices when
> operations can be merged. Even SSDs have fixed, per-command overheads and
> merging writes may help prevent fragmentation.  On drivers that support
> unmapped I/O, merging should be fairly cheap.
>
> It would be an interesting performance experiment.

In theory I'd agree but in practice this was not the case with bioq
becoming a noticable bottleneck for SSD based machines, hence this change.

The sysctl's still allow this to be configured :)

    Regards
    Steve

================================================
This e.mail is private and confidential between Multiplay (UK) Ltd. and the person or entity to whom it is addressed. In the event of misdirection, the recipient is prohibited from using, copying, printing or otherwise disseminating it or any information contained in it. 

In the event of misdirection, illegible or incomplete transmission please telephone +44 845 868 1337
or return the E.mail to postmaster at multiplay.co.uk.