You don't say so explicitly, I assume that you are using the standard
asyn device support, and that the ring buffer you are referring to is
the one in that device support?
> Even if we manage to 'disable' the processing inside the device driver
> (in terms that no new data is written to record buffers, I/O intr
> SCANing still active), it takes quite some time to process all the
> pending requests already in the ring buffers for the corresponding
How many records are involved? By default each record only has 10
elements in its ring buffer, so each record would process at most 10
times before the ring buffer was empty. This should be quite fast,
unless you have very many records in this state.
There is no way to tell it to flush the buffer.
However, you can decrease the size of the ring buffer, down to a single
element if you want. The ring buffer default size is 10 values, but
this can be changed on a per-record basis by setting the dbInfo string
"FIFO" to a different value. In your case you could set the value to
"1". The disadvantage of this is that if there are several callbacks in
rapid succession the record will only process on the last value, it will
not process with the other values. This may be OK in your case.
[mailto:email@example.com] On Behalf Of Hinko Kocevar
Sent: Thursday, May 26, 2011 4:06 AM
To: EPICS tech-talk
Subject: record ring buffer flushing
We are running EPICS 3.14.10 on ARM based system. Our device driver is
using asyn driver.
There are several records that are processed on I/O intr SCAN. Sometimes
the I/O rate is quite high and the system load (CPU) goes over the top,
with high (> 3.0) loadavg. When this happens IOC is sluggish to respond
to any CA requests.
Even if we manage to 'disable' the processing inside the device driver
(in terms that no new data is written to record buffers, I/O intr
SCANing still active), it takes quite some time to process all the
pending requests already in the ring buffers for the corresponding
Only then can we successfully use the CA to set/get any other PV on the
IOC, and not worry about the delayed response and/or timeouts.
Is there a way to tell IOC or a PV record to forget the pending
events/requests in its ring buffer (eg. some kind of flush)?
This way we could be sure that the IOC will be responding in timely
fashion, when we try to access some PV, and avoid waiting for the ring
buffer to empty by itself..
Has anyone dealt with similar situation?
Any comments and suggestions are welcomed!
Technical support software engineer
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