Re: EPICS Channel Access UDP Processing

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 5/23/25 08:06, Wells, Alex (DLSLtd,RAL,LSCI) via Tech-talk wrote:
> Hello Tech Talk,
>
> Could I please get some directions to the exact bit of code that processes a UDP message and iterates through the list of PVs to see if that IOC has it? I get as far as "camessage" in "camessage.c", but can't seem to find the next processing step.

For each UDP packet, there is an indirection through 'udpJumpTable[]' to reach udp_version_action()
once, and search_reply_udp() many times.  I expect that the majority of the time in the later will
be spent in 'dbChannelTest()' which does the hash table lookup of local record names.

https://urldefense.us/v3/__https://github.com/epics-base/epics-base/blob/c67982aa3f3660aace9832225b2e798317133db2/modules/database/src/ioc/rsrv/camessage.c*L2167__;Iw!!G_uCfscf7eWS!dBHoDebKrIPXx0d5NmypWg4DHjOBQrFoIjpXkWTGadJpih3EfoJDqUPtnlWQvXcRjetXWMWu7CEq_nKrbLMjosQ3fg$ 

> I ask as I think I need to implement tracing in this function (CASDEBUG doesn't give me enough). I have one particular IOC that is regularly using 20+% CPU on the "CAS-UDP" task (as reported by "rt cpuuse"). I will note that it works fine in two other near-identical IOCs, and has also reoccurred despite replacing a lot of the hardware, so I'm currently investigating whether it's an EPICS UDP software issue.
>
> For reference this is me continuing investigations started in this TechTalk thread: https://epics.anl.gov/tech-talk/2025/msg00318.php  <https://epics.anl.gov/tech-talk/2025/msg00318.php >
>
> Thank you,
> Alex Wells
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