Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Fri, 24 Jul 2009 09:11:58 +0200

At the moment, I have EPICS_CA_MAX_ARRAY_BYTES=4000000 on the gateway.

But I found that the gateway already became slow with about 10 arrays of 2000

double each, processing with 10 Hertz. So it's probably not a question of the

array length but of the total array elements per second.

But why should the gateway convert doubles to strings? A client that requests

numeric arrays as strings instead of the native format is quite stupid.

Dirk

Jeff Hill wrote:

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 [email protected]

<mailto:[email protected]>

LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

Message content: TSPA

*From:* Jeff Hill [mailto:[email protected]]
*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 [email protected]

<mailto:[email protected]>

LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

Message content: TSPA

--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System