High CPU usage with 5.x Linux kernel

[Alarig Le Lay]

Hi,

I recently upgraded from 4.19.97 to 5.4.28 and I noticed that bird was
using a lot more CPU (about three times).

On those two graphs you can see the CPU usage and when I rebooted:
https://pix.milkywan.fr/gallery#ugO0qVvx.png,ncr9kHfi.png

I rebooted to 4.19.113 and now I’m back to the ~10 % average CPU.

My router has 5 dual-stack fullviews (2 are from RRs), a dual-stack
OSPF and BFD on OSPF and on the RR sessions.

I also upgraded my RRs, but I don’t see any change on them, so the usage
might be related to FIB/kernel route insertion.

I don’t have other BGP implementation on my network, so it might be a
kernel bug and not a bird one. But on the other hand, I was clearly
seeing the bird process using a whole CPU core with htop.

I can share my .conf for each kernel if it’s helpful.

Regards,
-- 
Alarig