[dm-devel] Improve processing efficiency for addition and deletion of multipath devices

[Martin Wilck]

Hi Tang,

On Wed, 2016-11-16 at 16:45 +0800, tang.junhui at zte.com.cn wrote:

> I think we can merger most of uevent messages and reduce most of
> unnecessary DM change 
> uevent messages during creation/deletion of multipath devices by this
> way. 
> The method you mentioned I think that it is a little complex, and it
> not reduce the DM 
> addition/change/deletion uevent messages which consumed system high
> resource. 

Let me quickly introduce myself, I'm a new member of Hannes' team at
SUSE and new on this ML.

Apart from Hannes' proposal for more fine-grained locking, I can see
the following options:

 a) instead of kicking the uevent processing thread whenever anything
is queued, kick it in predefined time intervals (1 second, say). The
uevent processor would then accumulate all changes received since it
had been kicked last, and apply DM changes only when necessary. This
may need to be a config option because it could obviously lead to
delayed device setup in some configurations.

 b) the logic of a) could be improved by the uevent listener detecting
"event storms" and waiting for them to end before kicking the
processing thread. The details of the heuristics for "storms" would
need to be worked out, of course.

 c) sometimes several uevents for the same physical path occur in quick
succession. Normally it should be sufficient to filter these such that
only the last event is processed.

Regards,
Martin

-- 
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)