Cellular Network Infrastructure

Note: according to https://man7.org/linux/man-pages/man7/sched.7.html POSIX.1 requires support of only 32 distinct priority levels so it's probably better to stick to those instead of full Linux range 1 (low) to 99 (high).

msuraev , there's no "specific change" which made OsmoPCU time-sensitive, it always has been AFAICT. It's time sensitive because it acts as part of osmo-bts-trx (or direct phy in the case of sysmo/oc2g/lc15) and it is requested to send DL blocks at specific points in time (RTS), with a specific time deadline (the time advance), otherwise the DL block/burst is not prepared in time when having to send it over the air interface (specific FN+TN).

I usually use (and did most tests while heavily refactoring osmo-pcu) same rt prio for osmo-bts-trx and osmo-pcu. Having lower prio in osmo-pcu than in osmo-bts-trx makes no sense, since that means that osmo-bts-trx could starve osmo-pcu and hence PDCH blocks never sent at the right time but later than expected.

pespin wrote in #note-4:

Having lower prio in osmo-pcu than in osmo-bts-trx makes no sense, since that means that osmo-bts-trx could starve osmo-pcu and hence PDCH blocks never sent at the right time but later than expected.

I don't have a strong opinion here (running everything with default prio myself), but actually it could make sense to give osmo-bts-trx a higher priority. The main difference between osmo-bts-trx and osmo-pcu is that the former operates on bursts, while the later does on blocks of bursts. Because of that, osmo-bts-trx unblocks the select() loop at least 4 times more often than osmo-pcu.

why do you think it matters the amount of times the select loop is run? It doesn't matter if it works on bursts or blocks, it will send nothing correctly if the block from osmo-pcu doesn't arrive in time.
So yeah, you have higher prio to send stuff which didn't arrive because whoever was expected to provide them is not being scheduled ASAP.
As a reminder, rts-advance exists for a reason (BTS<->PCU), and by lowering osmo-pcu prio you are potentially asking for a higher rts-advance.