RE: epicsSnPrintf is very slow when converting string arrays in GDD's aitConvert.cc

["Jeff Hill" <johill@lanl.gov>]

 

Ø  0.000132 seconds per conversion  - is epicsSnPrintf() really that slow?

 

To answer my own question; no. I just finished adding cvtFastPerform.cpp to libCom/tests and it looks like double to string conversion take more like 3 uSec worst case which is about 44 times faster than calculated.

 

Nevertheless, I am curious. What is the largest array size being communicated via the gateways at SLAC and at PSI? This might become a big issue for arrays exceeding say one million elements (that are converted to strings by the gateway).

 

Still bug hunting.

 

Jeff
______________________________________________________
Jeffrey O. Hill           Email        johill@lanl.gov
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

 

Message content: TSPA

 

From: Jeff Hill [mailto:johill@lanl.gov]
Sent: Wednesday, July 22, 2009 6:13 PM
To: 'Dirk Zimoch'; 'Ralph Lange'; 'Ernest L. Williams Jr.'; 'Amedeo Perazzo'
Cc: 'Core-Talk'
Subject: epicsSnPrintf is very slow when converting string arrays in GDD's aitConvert.cc

 

All,

 

I have discovered that a PCAS hang can occur when clients are fetching very large arrays as strings. Just to convert the number of elements that fit in a very large EPICS_CA_MAX_ARRAY_SIZE buffer with epicsSnPrintf can take a very long time. It appears that this required about 33 seconds during testing with EPICS_CA_MAX_ARRAY_SIZE of 10,000,000. Based on that I calculate 33 / ( 10,000,000 / MAX_STRING_SIZE ) is 0.000132 seconds per conversion. Is epicsSnPrintf() really that slow?

 

The solution appears to be to use the cvtFast library where it is in range in GDD’s aitConvert.cc. The cvtFast functions are a bit scary in today’s world - because a buffer size isn’t passed in – BTW. The current workaround is to just not use them for buffer sizes below some threshold.

 

Jeff
______________________________________________________
Jeffrey O. Hill           Email        johill@lanl.gov
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

 

Message content: TSPA