[Bug 12752] megaraid-sas driver performance worse than on-board sata_nv

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=12752


Adam Radford <aradford@gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |aradford@gmail.com




--- Comment #2 from Adam Radford <aradford@gmail.com>  2011-06-10 23:05:02 ---
devsk,

I'm sorry about you not getting a response from the previous megaraid_sas
developer.  He was probably not watching bugzilla.kernel.org.

There is nothing in the driver that will 'throttle' the I/O on your PERC5
controller.

The software raid code sets various read-ahead values in the block layer
request_queues it sets up:

# grep -i "ra_pages" *
raid0.c:         * If an individual device has an ra_pages greater than the
raid0.c:                if (mddev->queue->backing_dev_info.ra_pages < 2*
stripe)
raid0.c:                        mddev->queue->backing_dev_info.ra_pages = 2*
stripe;
raid10.c:               if (mddev->queue->backing_dev_info.ra_pages < 2*
stripe)
raid10.c:                       mddev->queue->backing_dev_info.ra_pages = 2*
stripe;
raid5.c:                if (mddev->queue->backing_dev_info.ra_pages < 2 *
stripe)
raid5.c:                        mddev->queue->backing_dev_info.ra_pages = 2 *
stripe;
raid5.c:                        if
(conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
raid5.c:                               
conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;

Can you try setting some OS read-ahead values (on top of the controller doing
read-ahead) for the scsi device attached to your PERC5 controller and
re-running 
your tests?

i.e.:

/sbin/blockdev --getra /dev/sda (See what you have set currently)
/sbin/blockdev --setra 8192 /dev/sda (Set read ahead for sda to 8192 sectors)
/sbin/blockdev --setra 16834 /dev/sda (Set read ahead for sda to 16384 sectors)

This may cause more I/O to be issued to the card from the OS and may improve
your bonnie++ results.

-Adam

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