How to improve PVA put concurrency performance

[zhouyunbin]

I need to put lots of PV at the same time, which function I used is chan.put.set().exec()， but no matter how I use std::jthread or std::thread to achieve, it looks like always sequential execution at the bottom level. Is there a way to put the value without for waiting timeout?

[mdavidsaver]

Based on chan.put.set().exec() I think this is a question about https://github.com/mdavidsaver/pvxs . I will try to transfer the issue.

[sveseli]

The question is probably for pvxs client, but you could also try MultiChannel class from the pvaClientCPP module. Here is what one can expect when connecting to and retrieving data from 1000 CA channels running in an IOC on the same machine:

>>> from pvaccess import *
>>> cList = ['X%s' % i for i in range (1,1001)]
>>> import time
>>> from pvaccess import *
>>> cList = ['X%s' % i for i in range (1,1001)]
>>> mc = MultiChannel(cList, CA)
>>> t0 = time.time(); pv = mc.get(); t1 = time.time(); print(t1-t0)
0.27422356605529785
>>> t0 = time.time(); pv = mc.get(); t1 = time.time(); print(t1-t0)
0.05835700035095215
>>> t0 = time.time(); pv = mc.get(); t1 = time.time(); print(t1-t0)
0.055959224700927734

The initial request is a bit slower because it takes some time to connect to the PVs. Here is what happens with put:

>>> vList = [float(i) for i in range (1,1001)]
>>> t0 = time.time(); mc.putAsDoubleArray(vList); t1 = time.time(); print(t1-t0)
0.13571906089782715
>>> t0 = time.time(); mc.putAsDoubleArray(vList); t1 = time.time(); print(t1-t0)
0.13674354553222656

[mdavidsaver]

It looks like github.com doesn't allow transfer of issues between users. So I've opened mdavidsaver/pvxs#42 for further discussion.

To answer your question. Concurrent operations are easy. The exec() method immediately returns an Operation, which can then be stored. In one loop call exec() several times and store each Operations. Then in a second loop call wait() on each Operation. The source for the pvxget executable does this for GET operations. The code flow is the same for PUT.

https://github.com/mdavidsaver/pvxs/blob/dd2f076b4aa6dc63fb91980eda711eabee910696/tools/get.cpp#L104