Hi-ho, friends! I'm trying to tune network queues so that there's one queue per core, as recommended in many, many places. I've noticed that if I adjust the number of queues from the default AND adjust the IRQ affinities, then I get some percentage (varying from a small percent to 100%, seemingly proportional to the number of reduced queues) of packets not making it through. For my setup, I have a single 36 core Skylake processor with two dual port X710 NICs. All traffic coming in one one port of each NIC is redirected out the other port (traffic arrives on all four ports). 34 cores are isolated for network processing. I adjust the combined queues from the default of 36 down, and then map the IRQ associated with each queue to one of the 34 isolated cores. Everything works fine if I don't map the IRQs. For a minimum repro case, I reduced my program (reproduced below) to a blind redirector using a devmap (it doesn't even adjust MACs, which is not a problem as my DUT is directly connected to a measurement device in promiscuous mode) reproduced below. I use bpftool to load 4 copies of the program and pin them, use bpftool to configure the egress interface in the devmap, and then use ip link to attach the programs to the interfaces. I have played around with when I adjust the queue counts and IRQs (before attaching XDP programs, after, XDP attachment in the middle, etc.) and it doesn't seem to matter. But with any ordering, if I just don't remap the IRQs, everything works fine, and if I remap, I lose packets. Has anyone encountered anything like this? Does anyone know what might be causing it? How can I assign a single queue to a single core without using the default number of queues and without losing packets? Thanks! --Zvi #include <linux/bpf.h> struct bpf_map_def { unsigned int type; unsigned int key_size; unsigned int value_size; unsigned int max_entries; unsigned int map_flags; struct bpf_map_def* inner_map; }; struct bpf_map_def __attribute__((section("maps"), used)) device_map = { .type = BPF_MAP_TYPE_DEVMAP, .key_size = sizeof(__u32), .value_size = sizeof(__u32), .max_entries = 1, }; static int (*bpf_redirect_map)(void *map, int key, int flags) = (void *)BPF_FUNC_redirect_map; __attribute__((section("xdp/test"), used)) int test(struct xdp_md *context) { __u32 key = 0; bpf_redirect_map(&device_map, key, 0); return XDP_REDIRECT; }