Re: Channel connection performance

["Hu, Yong via Tech-talk" <tech-talk at aps.anl.gov>]

On an ordinary Linux server, I did a few tests using cothread, which is a python binding of EPICS V3 Channel Access. And I got similar results as Sinisa got:

 

# Firstly, get a list of PVs (i.e. from a file). Connecting to 1269 PVs (which are from lots of different IOCs) takes about 0.3-seconds

>>> len(pvs)

1269

>>> pvs[:10]

['ACC-TS{EVG-AcTrig}Bypass-Sel', 'ACC-TS{EVG-AcTrig}Divider-SP', 'ACC-TS{EVG-AcTrig}Phase-SP', 'ACC-TS{EVG-AcTrig}SyncSrc-Sel', 'ACC-TS{EVG-Dbus:0}Map-Sel', 'ACC-TS{EVG-Dbus:0}MapConv-Sel_', 'ACC-TS{EVG-Dbus:0}Omsl-FOut', 'ACC-TS{EVG-Dbus:0}Src-Sel', 'ACC-TS{EVG-Dbus:1}Map-Sel', 'ACC-TS{EVG-Dbus:1}MapConv-Sel_']

>>> from cothread.catools import connect

>>> import time

>>> t0=time.time(); results = connect(pvs, cainfo=True, throw=False); t1=time.time(); print(t1-t0)

0.299956083298

 

# another test on 38380 PVs: connection takes less than 7-seconds

>>> len(pvs)

38380

>>> t0=time.time(); results = connect(pvs, cainfo=True, throw=False); t1=time.time(); print(t1-t0)

6.67425608635

 

http://controls.diamond.ac.uk/downloads/python/cothread/

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Reply-To: "Veseli, Sinisa" <sveseli at anl.gov>
Date: Monday, January 25, 2021 at 3:48 PM
Cc: "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Subject: Re: Channel connection performance

 

Hi,

 

If you are already using pvaClientCPP, you could also take a look at the MultiChannel class (examples can be found here: https://github.com/epics-base/exampleCPP/tree/master/exampleClient/src)

 

 

Here is how long it takes on my machine to connect and retrieve values for 1000 CA channels using pvapy (both client and IOC are running on the same machine):

 

>>> import time

>>> from pvaccess import *

>>> cList = ['X%s' % i for i in range (1,1001)]

>>> c = MultiChannel(cList, CA)

>>> t0 = time.time(); pv=c.get(); t1=time.time() ; print(t1-t0)

0.21088194847106934

>>>

 

Sinisa

 

 

--

Siniša Veseli

Scientific Software Engineering & Data Management

Advanced Photon Source

Argonne National Laboratory

sveseli at anl.gov

(630)252-9182

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>
Sent: Monday, January 25, 2021 2:19 PM
To: Axel Terfloth <terfloth at itemis.de>
Cc: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Channel connection performance

 

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