[dm-devel] [PATCH 01/18] libmultipath: Add prioritizer context data

[Hannes Reinecke]

On 10/08/2015 09:44 PM, Benjamin Marzinski wrote:
> Currently, running the alua prioritizer on a path causes 5 ioctls on many
> devices.  get_target_port_group_support() returns whether alua is
> supported. get_target_port_group() gets the TPG id. This often takes two
> ioctls because 128 bytes is not a large enough buffer size on many
> devices. Finally, get_asymmetric_access_state() also often takes two
> ioctls because of the buffer size. This can get to be problematic when
> there are thousands of paths.  The goal of this patch to to cut this down
> to one call in the usual case.
> 
> In order to do this, I've added a context pointer to the prio structure,
> similar to what exists for the checker structure, and initprio() and
> freeprio() functions to the prioritizers. The only one that currently uses
> these is the alua prioritizer. It caches the type of alua support, the TPG
> id, and the necessary buffer size.  The only thing I'm worried about with
> this patch is whether the first two values could change.  In order to deal
> with that possibility, whenever a path gets a change event, or becomes
> valid again after a failure, it resets the context structure values, which
> forces all of them to get checked the next time the prioritizer is called.
> 
Hmm. What about reading /sys/block/sdX/device/vpg_pg83 ?
That carries the same information, and you would need to call the
ioctl only once ...

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare at suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)