> Date: Sat, 27 Sep 2025 18:36:50 +0200
> From: Alexander Bluhm <bluhm@openbsd.org>
> 
> Hi,
> 
> Currently most network drivers use 8 queues and distribute interrupts.
> ix(4) is the only one that may allocate more than 8.  ice(8) uses
> only 8 vectors, but allocates more interrupts.
> 
> I would like to limit interrupts and queues to 8 for all drivers.
> This prevents running out of interrupt vectors so easily.

Here's a nickel boy; go buy yourself a better computer!

Joking aside, we shouldn't waste resources and I it is plausible that
using the maximum number of queues provided by the hardware isn'
optimal.

> Currently we have 8 softnet threads which limits parallel processing
> anyway.  We can tune these values later.

Does it even make sense to have more rx queues than softnet threads?
Should there be a single limit for both?

> With this diff, forwarding througput increases from 45 to 50 GBit/sec
> on my 12 core machine from ice0 to ice1.  I am using iperf3 TCP on
> Linux to measure it.  I think slower performance happend because
> ice(4) was allocating more interrupts than it has vectors.  Now
> everything is limited to 8.  For other drivers I see no difference
> as they operate at line speed anyway.
> 
> I think arbitrary numbers IXL_MAX_VECTORS, IGC_MAX_VECTORS and
> IGC_MAX_VECTORS could go away, but that would be per driver diffs.
> 
> Second part of the diff spreads the interrupts of network devices
> equally over the softnet tasks.

That is this line:

> -	ifq->ifq_softnet = net_tq(idx);
> +	ifq->ifq_softnet = net_tq(ifp->if_index * IF_MAX_VECTORS + idx);

Does this even do anything given that both IF_MAX_VECTOR and the
number of softneq threads is 8?  Doesn't this simply reduce to:

    (ifp->if_index * 8 + idx) % 8 = idx

Maybe it is better to stagger the interrupts instead?  Like

    ifq->ifq_softnet = net_tq(ifp->if_index + idx);

?


> Index: dev/pci/if_bnxt.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_bnxt.c,v
> diff -u -p -r1.56 if_bnxt.c
> --- dev/pci/if_bnxt.c	5 Sep 2025 09:58:24 -0000	1.56
> +++ dev/pci/if_bnxt.c	25 Sep 2025 08:27:45 -0000
> @@ -545,9 +545,11 @@ bnxt_attach(struct device *parent, struc
>  		nmsix = pci_intr_msix_count(pa);
>  		if (nmsix > 1) {
>  			sc->sc_ih = pci_intr_establish(sc->sc_pc, ih,
> -			    IPL_NET | IPL_MPSAFE, bnxt_admin_intr, sc, DEVNAME(sc));
> -			sc->sc_intrmap = intrmap_create(&sc->sc_dev,
> -			    nmsix - 1, BNXT_MAX_QUEUES, INTRMAP_POWEROF2);
> +			    IPL_NET | IPL_MPSAFE, bnxt_admin_intr, sc,
> +			    DEVNAME(sc));
> +			sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix - 1,
> +			    MIN(BNXT_MAX_QUEUES, IF_MAX_VECTORS),
> +			    INTRMAP_POWEROF2);
>  			sc->sc_nqueues = intrmap_count(sc->sc_intrmap);
>  			KASSERT(sc->sc_nqueues > 0);
>  			KASSERT(powerof2(sc->sc_nqueues));
> Index: dev/pci/if_ice.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ice.c,v
> diff -u -p -r1.59 if_ice.c
> --- dev/pci/if_ice.c	17 Sep 2025 12:54:19 -0000	1.59
> +++ dev/pci/if_ice.c	27 Sep 2025 07:35:25 -0000
> @@ -30501,7 +30501,8 @@ ice_attach_hook(struct device *self)
>  	sc->sc_nmsix = nmsix;
>  	nqueues_max = MIN(sc->isc_nrxqsets_max, sc->isc_ntxqsets_max);
>  	sc->sc_intrmap = intrmap_create(&sc->sc_dev, sc->sc_nmsix - 1,
> -	    nqueues_max, INTRMAP_POWEROF2);
> +	    MIN(MIN(nqueues_max, ICE_MAX_VECTORS), IF_MAX_VECTORS),
> +	    INTRMAP_POWEROF2);
>  	nqueues = intrmap_count(sc->sc_intrmap);
>  	KASSERT(nqueues > 0);
>  	KASSERT(powerof2(nqueues));
> Index: dev/pci/if_igc.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_igc.c,v
> diff -u -p -r1.28 if_igc.c
> --- dev/pci/if_igc.c	24 Jun 2025 11:00:27 -0000	1.28
> +++ dev/pci/if_igc.c	27 Sep 2025 07:29:57 -0000
> @@ -724,8 +724,8 @@ igc_setup_msix(struct igc_softc *sc)
>  	/* Give one vector to events. */
>  	nmsix--;
>  
> -	sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix, IGC_MAX_VECTORS,
> -	    INTRMAP_POWEROF2);
> +	sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix,
> +	    MIN(IGC_MAX_VECTORS, IF_MAX_VECTORS), INTRMAP_POWEROF2);
>  	sc->sc_nqueues = intrmap_count(sc->sc_intrmap);
>  }
>  
> Index: dev/pci/if_ix.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ix.c,v
> diff -u -p -r1.221 if_ix.c
> --- dev/pci/if_ix.c	24 Jun 2025 11:02:03 -0000	1.221
> +++ dev/pci/if_ix.c	25 Sep 2025 08:27:45 -0000
> @@ -1854,7 +1854,8 @@ ixgbe_setup_msix(struct ix_softc *sc)
>  	/* XXX the number of queues is limited to what we can keep stats on */
>  	maxq = (sc->hw.mac.type == ixgbe_mac_82598EB) ? 8 : 16;
>  
> -	sc->sc_intrmap = intrmap_create(&sc->dev, nmsix, maxq, 0);
> +	sc->sc_intrmap = intrmap_create(&sc->dev, nmsix,
> +	    MIN(maxq, IF_MAX_VECTORS), 0);
>  	sc->num_queues = intrmap_count(sc->sc_intrmap);
>  }
>  
> Index: dev/pci/if_ixl.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/dev/pci/if_ixl.c,v
> diff -u -p -r1.109 if_ixl.c
> --- dev/pci/if_ixl.c	17 Sep 2025 12:54:19 -0000	1.109
> +++ dev/pci/if_ixl.c	27 Sep 2025 07:29:57 -0000
> @@ -1782,8 +1782,9 @@ ixl_attach(struct device *parent, struct
>  		if (nmsix > 1) { /* we used 1 (the 0th) for the adminq */
>  			nmsix--;
>  
> -			sc->sc_intrmap = intrmap_create(&sc->sc_dev,
> -			    nmsix, IXL_MAX_VECTORS, INTRMAP_POWEROF2);
> +			sc->sc_intrmap = intrmap_create(&sc->sc_dev, nmsix,
> +			    MIN(IXL_MAX_VECTORS, IF_MAX_VECTORS),
> +			    INTRMAP_POWEROF2);
>  			nqueues = intrmap_count(sc->sc_intrmap);
>  			KASSERT(nqueues > 0);
>  			KASSERT(powerof2(nqueues));
> Index: net/if.h
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/net/if.h,v
> diff -u -p -r1.221 if.h
> --- net/if.h	9 Sep 2025 09:16:18 -0000	1.221
> +++ net/if.h	25 Sep 2025 08:27:45 -0000
> @@ -526,6 +526,9 @@ struct if_sffpage {
>  #include <net/if_arp.h>
>  
>  #ifdef _KERNEL
> +
> +#define IF_MAX_VECTORS		8
> +
>  struct socket;
>  struct ifnet;
>  struct ifq_ops;
> Index: net/ifq.c
> ===================================================================
> RCS file: /data/mirror/openbsd/cvs/src/sys/net/ifq.c,v
> diff -u -p -r1.62 ifq.c
> --- net/ifq.c	28 Jul 2025 05:25:44 -0000	1.62
> +++ net/ifq.c	25 Sep 2025 08:27:45 -0000
> @@ -255,7 +255,7 @@ void
>  ifq_init(struct ifqueue *ifq, struct ifnet *ifp, unsigned int idx)
>  {
>  	ifq->ifq_if = ifp;
> -	ifq->ifq_softnet = net_tq(idx);
> +	ifq->ifq_softnet = net_tq(ifp->if_index * IF_MAX_VECTORS + idx);
>  	ifq->ifq_softc = NULL;
>  
>  	mtx_init(&ifq->ifq_mtx, IPL_NET);
> 
>