Re: Channel connection performance

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 1/25/21 11:00 AM, Axel Terfloth via Tech-talk wrote:
> Hello,
> 
> i’m new to EPICS and take a closer look at it for evaluation purpose. To obtain a better understanding I started to dig deeper by implementing some tests which are based on the C++ examples. From a functional point of view everything I tried works nicely so far. Also the performance is generally very good in most of my test scenarios. Nevertheless one issue i came across is the time required for connecting to a channel  via PVA. In this scenario I set up 4000 process variables and implement one client which implements high frequency put and get access to a quarter (1000) of these proces variables. On my machine (which runs all processes for now) if takes about 250ms for a single channel connection. Once all channels are connected is really fast. Nevertheless connecting 1000 pvs takes more than 6 minutes. I currently connect channel by channel using the PvaClient API in my tests. Is there a more efficient way to connect to a large set of channels?  I would appreciate any hint.
Can you be more specific about what you application is doing?  A common source
of slowdown with CA or PVA clients is for user code the is to perform network
operations in sequence.  This can be done in parallel, which can give a nice speedup.


You might want to investigate my new (hopefully replacement) PVA library
which makes it easy to run many operations in parallel.

https://mdavidsaver.github.io/pvxs/

eg. the equivalent of 'pvget'

https://github.com/mdavidsaver/pvxs/blob/d0e82744d30256e36585b51af2704cc01a938e18/tools/get.cpp#L109-L132


If this isn't an option, then is the 'pvac' wrapper API which provides a
similar abstraction, though with more verbose syntax.

http://epics-base.github.io/pvAccessCPP/

eg. parallel get operations

http://epics-base.github.io/pvAccessCPP/examples_getme.html