On Fri, 22 Apr 2022 02:02:21 +0200 "Jason A. Donenfeld" <Jason@xxxxxxxxx> wrote: > 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 Applications like DPDK that do polling often use isolcpus or cgroups to keep unwanted rabble off of their cpus. Having wireguard use those cpus seems bad.
