Copying from the old thread [18.06.4] speed fix for BT HomeHub 5a, since this won't be changed for 18.06.X or 19.07.X as it's a "performance fix" the quickest way on an existing device is just to;
$ rm /etc/hotplug.d/net/20-smp-tune
This won't affect currently up interfaces until a restart or you manually echo 0 to their rps_cpus and xps_cpus proc entries.
If building from git master then no action is required as it's already fixed. For a HH5 to further improve performance, I would suggest adding the SMP IRQ patches, now just one 0901-add-icu-smp-support.patch for git master which really should be commited, and then use the irqbalance daemon or manually set IRQ assignments in /etc/rc.local.