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

[Zdenek Kabelac]

Dne 28.11.2016 v 17:07 Benjamin Marzinski napsal(a):
> On Mon, Nov 28, 2016 at 11:05:29AM +0100, Hannes Reinecke wrote:
>> Hi Junhui,
>>
>> Tricky bit would be to figure out _when_ to stop uevent processing and
>> calling 'ev_add_path'.
>> I guess we'd need to make 'ev_add_path' running in a separate thread;
>> that way we'd be putting pressure off the uevent processing thread and
>> the whole thing should be running far smoother.
>
> I still think that we don't need to force a wait here.
> uevent_dispatch() already pulls off all the queued events in a batch. We
> could just merge over the batch that we are given.  This has the nice
> property that when uevents aren't coming in a storm, we quickly process
> the next event, and when they are, the further multipathd gets behind, the
> larger the list it will merge over.
>


It's worth to mention at this point   - libdevmapper  1.02  is NOT library
with multithread support - there is 'certain' limited set of thread-safe 
functions, but for sure not a whole library.

So any threaded usage of libdevmapper.so would likely require mutex against
access to do library code.

Regards

Zdenek