high ksoftirqd while using module gtp?

Dear All, I've been using the GTP-U kernel module to communicate with a P-GW. Running Fedora 29, kernel 4.18.16-300.fc29.x86_64. At high traffic levels through the GTP-U tunnel I see the performance degrade as 100% CPU is consumed by a single ksoftirqd process. It is running on a multi-cpu machine and as far as I can tell the load is evenly spread across the cpus (ie either manually via smp_affinity, or even irqbalance, checking /proc/interrupts so forth.). Has anyone else experienced this? Is there any particular area you could recommend I investigate to find the root cause of this bottleneck, as i'm starting to scratch my head where to look next... Thanks in advance Tony ---- FYI modinfo gtp filename: /lib/modules/4.18.16-300.fc29.x86_64/kernel/drivers/net/gtp.ko.xz alias: net-pf-16-proto-16-family-gtp alias: rtnl-link-gtp description: Interface driver for GTP encapsulated traffic author: Harald Welte <hwelte(a)sysmocom.de> license: GPL depends: udp_tunnel retpoline: Y intree: Y name: gtp vermagic: 4.18.16-300.fc29.x86_64 SMP mod_unload modinfo udp_tunnel filename: /lib/modules/4.18.16-300.fc29.x86_64/kernel/net/ipv4/udp_tunnel.ko.xz license: GPL depends: retpoline: Y intree: Y name: udp_tunnel vermagic: 4.18.16-300.fc29.x86_64 SMP mod_unload