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<== Date ==> <== Thread ==>

Subject: RE: CA Priority for PV Gateway
From: "Jeff Hill" <[email protected]>
To: "'Andrew Johnson'" <[email protected]>, "'Ernest L. Williams Jr.'" <[email protected]>
Cc: "'Core-Talk'" <[email protected]>
Date: Tue, 21 Jul 2009 18:59:34 -0600
In an ideal world it might work like this. The priority of the gateway's
particular IOC channel would be the maximum of the priority of each of the
attached client channels, but no greater than a maximum priority specified
in the access security system.

This is somewhat harder for the GW to implement however because if the
priority changed because a new client attached to the channel then the GW
would need to seamlessly create a new IOC channel, move the preexisting
attached client channels to the new IOC channel when it connects, and then
destroy the old IOC channel.

Access security based maximums for channel priorities are of course also
needed in IOC so there is good opportunity for code sharing.

Jeff
______________________________________________________
Jeffrey O. Hill           Email        [email protected]
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

Message content: TSPA


> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
> On Behalf Of Andrew Johnson
> Sent: Tuesday, July 21, 2009 1:50 PM
> To: Ernest L. Williams Jr.
> Cc: Core-Talk
> Subject: Re: CA Priority for PV Gateway
> 
> Hi Ernest,
> 
> On Tuesday 21 July 2009 11:29:37 Ernest L. Williams Jr. wrote:
> >
> > Shouldn't connection that the PV gateway has to IOCs be attached with a
> > high CA Priority?
> 
> Not necessarily, that probably depends on the design of your control
> system.
> If you only have OPI connections coming through the gateway the current
> setting is probably right.
> 
> > How do we change this?
> 
> The priority of any CA channel connection is controlled by the client when
> it
> connects to the PV, so the gateway could request a higher priority for the
> channels on its client-side if it was coded to do so.  However both the
> calls
> to ca_create_channel() in the gateway code currently specify the fixed
> value
> CA_PRIORITY_DEFAULT for their priority.  Note that changing the priority
> of
> your clients can have undesirable effects within the IOCs though if you're
> not careful.
> 
> One quick way to raise the priority of your gateway channels would be to
> rebuild the gateway to use something like CA_PRIORITY_ARCHIVE instead,
> although this would then affect all PVs on all IOCs that the gateway
> connects
> to.
> 
> Better solutions might be to add a command-line argument to configure that
> fixed value (similar to the  -p <prio>  option Ralph recently added to the
> caget, caput, camonitor and cainfo programs in Base), or even to make it
> controllable through the gateway's configuration file on a per-channel
> (regexp) basis.
> 
> I believe CosyLab has experience in making changes to the gateway code if
> you
> don't have any effort available to do that in-house.
> 
> - Andrew
> --
> The best FOSS code is written to be read by other humans -- Harold Welte



References:
Re: CA Priority for PV Gateway Andrew Johnson

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