Re: [PATCH RESEND 6/18] megaraid_sas : Use Block layer tag support for internal command indexing

[Hannes Reinecke <hare@suse.de>]

On 04/20/2015 02:33 PM, Sumit.Saxena@avagotech.com wrote:
> megaraid_sas driver will use block layer provided tag for indexing internal MPT frames to get any unique MPT frame tied with tag.
> Each IO request submitted from SCSI mid layer will get associated MPT frame from MPT framepool (retrieved and return back using spinlock
> inside megaraid_sas driver's submission/completion call back). Getting MPT frame from MPT Frame pool is very expensive operation because 
> of associated spin lock operation (spinlock overhead increase on multi NUMA node). This type of locking in driver is very expensive
> call considering each IO request need - Acquire and Release of the same lock.
> 
> With this support, in IO path driver will directly provide the unique command index(which is based on block layer tag)
> and will get the MPT frame tied to the tag and this way driver can get rid off lock, which synchronizes the access to MPT frame pool 
> while fetching and returning MPT frame from the pool.
> 
> This support in driver provides siginificant performance improvement(on multi NUMA node system)on latest upstream with SCSI.MQ
> as well as on existing linux distributions.
> Here is the data for test executed at Avago-
> - IO Tool- FIO
> - 4 Socket SMC server. (4 NUMA node server)
> - 12 SSDs in JBOD mode .
> - 4K Rand READ, QD=32
> - SCSI MQ x86_64 (Latest Upstream kernel)
> - upto 300% Performance Improvement.
> 
> If IOs are running on single Node, perfromance gain is less, but as soon as increase number of nodes, performance improvement
> is significant. IOs running on all 4 NUMA nodes, with this patch applied IOPs observed was  1170K vs 344K IOPs seen without this patch.
> 
> Signed-off-by: Kashyap Desai <kashyap.desai@avagotech.com>
> Signed-off-by: Sumit Saxena <sumit.saxena@avagotech.com>
> ---
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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