Experimental Physics and
Industrial Control System

Dirk,

Dirk Zimoch wrote:

our vxWorks IOCs mount their boot directory, auto-save-and-restore directory and data aquisition directory via NFS.

Now, I noticed a very poor performance on several IOCs. Test

...

I have also observed this when comparing to a NFS client I wrote
for the RTEMS (open source) RTOS. My client is simple and similar
in performance (i.e., low perf.). This is mostly due to the lack
of a buffer cache (read-ahead / delayed write) which could significantly
increase performance. Maybe, vxWorks has no buffer cache either.
It means that network I/O is essentially synchronous, implying
a full RPC call for every read/write request!

You could try to only use buffered I/O with large buffers and
increase NFS packets (if possible under vxWorks) to the protocol
limit of <~8k. Try this + using stdio with a custom buffer
taylored to the NFS packet size (setvbuf(3)).

When only vxWorks is running but not EPICS, it seems to be ok. If an empty EPICS (no records) is running, there few errors. The problem does not depend on the EPICS version (I tried 3.13.2 and 3.13.9). The idle time of the ioc is about 80%.

The NFS protocol version supported by vxWorks uses UDP packets for data transfer, and is not as efficient at handling dropped packets as TCP is. In your case, I suspect that your IOCs are dropping input packets from the network, which causes the 5 second NFS delays.

Since your IOC has lots of idle time available, you should be able to resolve this by just increasing the size of the network input buffer pool, which is usually one of the parameters in the vxWorks END configuration string - have a look in your sysEnd.c file [or wherever the xxxEndLoad() routine is called in your BSP] and increase the number of read buffers.

- Andrew

References:

NFS performance problems on vxWorks Dirk Zimoch

Re: NFS performance problems on vxWorks Andrew Johnson

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