Re: Prioritizing Channel Access per Record?

[Brian Bevins <bevins@jlab.org>]

On 03/18/14 13:00, Ralph Lange wrote:
> On 18.03.2014 17:30, Brian Bevins wrote:
> > The waveforms are soft records that have their buffers filled by 
> > dedicated threads, which then post events to process the records.
> > I only see the slowdown when a client is connected to the waveforms. 
> > Even with the waveform records processing normally, the "fast" 
> > records update normally as long as no CA clients monitor the 
> > waveforms. I interpreted this to mean that the CA traffic was the 
> > bottleneck, but maybe I'm wrong.
> Hmmm... another idea:
>
> Please check that you have no database links that would pull "fast" 
> and "slow" records into the same lock set.
> During record processing, waveforms are put in the CA send queue by 
> reference, while atomic data is put directly into the queue.
> When the low-priority CA send thread later-on copies the data out of 
> the record into the network buffer, it has to lock the record. (It can 
> just copy from the queue for atomic data, which does not require 
> locking.)
> Possible effect: if your database has link connections that pull 
> waveform records and "fast" records into the same lock set, the "fast" 
> records might block while CA copies data from the waveforms.
> Perfectly harmless looking things, like SDIS links pointing to the 
> same "disable" record, may easily pull far too many records into the 
> same lock set.
> Making this kind of links ".CA" often helps by breaking up the lock 
> sets without affecting function.
On 03/18/14 13:14, Andrew Johnson wrote:
> The IOC shell 'dblsr' command shows you the IOC's lock-sets.
>
> 'dblsr * 1' will print all the lock-sets and their members, while 'dblrs
> * 2' shows you the links between the records as well. Unfortunately the
> output is a bit noisy. You can use a specific record name instead of the
> * to see just the lock-set containing that record.
A very good point. I checked all the lock sets and each of my "fast" 
records and each of my waveforms is in its own set.
--
Brian S. Bevins, PE
Computer Scientist / Mechanical Engineer
Thomas Jefferson National Accelerator Facility

     "The urge to save humanity is almost always only a false-face
      for the urge to rule it."
                                     -- H. L. Mencken