From: Alexander Bluhm <bluhm@openbsd.org>
Subject: softnet 8 threads
To: tech@openbsd.org
Date: Fri, 18 Jul 2025 00:40:02 +0200

Hi,

After unlocking the hot path of the network stack, I would like to
increase the number of softnet threads.  I think 8 insted of 4 would
be a good number.  Note that it is capped by number of CPU.

On a 12 core machine, I receive 30 TCP streams from two Linux
machines.  With 4 softnet threads I see 40 GBit/sec combined, and
8 threads increase it to 50 Gbit/sec.

ok?

bluhm

Index: net/if.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/net/if.c,v
diff -u -p -r1.737 if.c
--- net/if.c	7 Jul 2025 02:28:50 -0000	1.737
+++ net/if.c	17 Jul 2025 09:42:50 -0000
@@ -239,7 +239,7 @@ struct softnet {
 	struct taskq	*sn_taskq;
 	struct netstack	 sn_netstack;
 } __aligned(64);
-#define NET_TASKQ	4
+#define NET_TASKQ	8
 struct softnet	softnets[NET_TASKQ];
 
 struct task	if_input_task_locked = TASK_INITIALIZER(if_netisr, NULL);