From: Vitaliy Makkoveev <mvs@openbsd.org>
Subject: Re: softnet 8 threads
To: Alexander Bluhm <bluhm@openbsd.org>
Cc: tech@openbsd.org
Date: Fri, 18 Jul 2025 02:08:47 +0300

On Fri, Jul 18, 2025 at 12:40:02AM +0200, Alexander Bluhm wrote:
> 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?
> 

Makes sense.

> 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);
>