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

[Martin Wilck]

On Fri, 2016-11-18 at 16:26 -0600, Benjamin Marzinski wrote:

> The issue is that we simply need to work on processing the whole list
> at
> a time.  Martin's filtering definitely has a place here. He is
> correct
> that if we get a delete uevent for a device, we don't need to process
> any of the earlier ones.  We do need to look at both the add and
> change
> uevents individually. For instance, one of the change uevents out of
> a
> group could be for changing the read-only status of a device. If we
> just
> took the most recent, we would miss that information.  The good news
> is
> that we don't need to actually call uev_add_path and uev_update_path
> once for each of these events.  All we need to do is read through the
> uev environment variables for all of them to find the information we
> need (like change in ro status), and then call the function once with
> that information.

Do we need to implement the environment-merging ourselves? AFAICS this
logic is implemented in udev itself. So if the last event for a given
device is a change event, we'd just need to fetch the device properties
from the udev db. Therefore IMO we just have to look at the last
received event for a given path:

 - DELETE => discard the device
 - ADD => use the udev properties coming with the event
 - CHANGE => query udev db for current set of properties
 
> At any rate, I'd rather get rid of the gazillion waiter threads
> first.

Hm, I thought the threads are good because this avoids one unresponsive
device to stall everything?

Martin

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