netdev@ - Original thread is at https://lore.kernel.org/wireguard/20220405212129.2270-1-cf.natali@xxxxxxxxx/ Hi Charles-François, On Tue, Apr 05, 2022 at 10:21:29PM +0100, Charles-Francois Natali wrote: > WireGuard currently uses round-robin to dispatch the handling of > packets, handling them on all online CPUs, including isolated ones > (isolcpus). > > This is unfortunate because it causes significant latency on isolated > CPUs - see e.g. below over 240 usec: > > kworker/47:1-2373323 [047] 243644.756405: funcgraph_entry: | > process_one_work() { kworker/47:1-2373323 [047] 243644.756406: > funcgraph_entry: | wg_packet_decrypt_worker() { [...] > kworker/47:1-2373323 [047] 243644.756647: funcgraph_exit: 0.591 us | } > kworker/47:1-2373323 [047] 243644.756647: funcgraph_exit: ! 242.655 us > | } > > Instead, restrict to non-isolated CPUs. Huh, interesting... I haven't seen this feature before. What's the intended use case? To never run _anything_ on those cores except processes you choose? To run some things but not intensive things? Is it sort of a RT-lite? I took a look in padata/pcrypt and it doesn't look like they're examining the housekeeping mask at all. Grepping for housekeeping_cpumask doesn't appear to show many results in things like workqueues, but rather in core scheduling stuff. So I'm not quite sure what to make of this patch. I suspect the thing to do might be to patch both wireguard and padata, and send a patch series to me, the padata people, and netdev@xxxxxxxxxxxxxxx, and we can all hash this out together. Regarding your patch, is there a way to make that a bit more succinct, without introducing all of those helper functions? It seems awfully verbose for something that seems like a matter of replacing the online mask with the housekeeping mask. Jason
