From: Chris Cappuccio <chris@nmedia.net>
Subject: Re: vio: Enable multiqueue
To: Stefan Fritsch <sf@openbsd.org>
Cc: Hrvoje Popovski <hrvoje@srce.hr>, tech@openbsd.org
Date: Sun, 26 Jan 2025 12:59:13 -0800

Stefan Fritsch [sf@openbsd.org] wrote:
> 
> diff --git a/sys/net/ifq.c b/sys/net/ifq.c
> index 7368aa50a57..547cfb26d84 100644
> --- a/sys/net/ifq.c
> +++ b/sys/net/ifq.c
> @@ -903,6 +903,8 @@ priq_idx(unsigned int nqueues, const struct mbuf *m)
>  
>  	if (ISSET(m->m_pkthdr.csum_flags, M_FLOWID))
>  		flow = m->m_pkthdr.ph_flowid;
> +	else
> +		flow = cpu_number();
>  
>  	return (flow % nqueues);
>  }


If you generalize the idea of pf_pkt_hash, and stick it in the wrong place,
it might look like this.

Index: ifq.c
===================================================================
RCS file: /cvs/src/sys/net/ifq.c,v
retrieving revision 1.55
diff -u -p -u -r1.55 ifq.c
--- ifq.c	20 Nov 2024 02:18:45 -0000	1.55
+++ ifq.c	26 Jan 2025 20:54:51 -0000
@@ -29,6 +29,11 @@
 #include <net/if.h>
 #include <net/if_var.h>
 
+#include <net/toeplitz.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
+
 #if NBPFILTER > 0
 #include <net/bpf.h>
 #endif
@@ -892,6 +897,60 @@ net_ifiq_sysctl(int *name, u_int namelen
 	return (error);
 }
 
+unsigned int
+ifq_pkt_hash(const struct mbuf *m)
+{
+	unsigned int hash = 0;
+	uint8_t ip_version;
+	const uint16_t *ports = NULL;
+	const struct ip *ip_hdr;
+	const struct ip6_hdr *ip6_hdr;
+	uint8_t proto = 0;
+
+	ip_version = (*mtod(m, uint8_t *) >> 4);
+	switch (ip_version) {
+	case 4:
+		ip_hdr = mtod(m, const struct ip *);
+		if (m->m_len < (ip_hdr->ip_hl << 2)) {
+			return 0;
+		}
+		hash ^= ip_hdr->ip_src.s_addr;
+		hash ^= ip_hdr->ip_dst.s_addr;
+		proto = ip_hdr->ip_p;
+		if (proto == IPPROTO_TCP || proto == IPPROTO_UDP) {
+			ports = (const uint16_t *)((uint8_t *)ip_hdr +
+			    (ip_hdr->ip_hl << 2));
+			hash ^= *(const uint32_t *)ports;
+		}
+		break;
+	case 6:
+		ip6_hdr = mtod(m, const struct ip6_hdr *);
+		if (m->m_len < sizeof(struct ip6_hdr)) {
+			return 0;
+		}
+		hash ^= ip6_hdr->ip6_src.__u6_addr.__u6_addr32[0];
+		hash ^= ip6_hdr->ip6_src.__u6_addr.__u6_addr32[1];
+		hash ^= ip6_hdr->ip6_src.__u6_addr.__u6_addr32[2];
+		hash ^= ip6_hdr->ip6_src.__u6_addr.__u6_addr32[3];
+		hash ^= ip6_hdr->ip6_dst.__u6_addr.__u6_addr32[0];
+		hash ^= ip6_hdr->ip6_dst.__u6_addr.__u6_addr32[1];
+		hash ^= ip6_hdr->ip6_dst.__u6_addr.__u6_addr32[2];
+		hash ^= ip6_hdr->ip6_dst.__u6_addr.__u6_addr32[3];
+		proto = ip6_hdr->ip6_nxt;
+		if (proto == IPPROTO_TCP || proto == IPPROTO_UDP) {
+			ports = (const uint16_t *)((uint8_t *)ip6_hdr +
+			    sizeof(struct ip6_hdr));
+			hash ^= *(const uint32_t *)ports;
+		}
+		break;
+	default:
+		return stoeplitz_n32(*(const uint32_t *)
+		    mtod(m, const uint8_t *));
+	}
+
+	return stoeplitz_n32(hash);
+}
+
 /*
  * priq implementation
  */
@@ -903,6 +962,8 @@ priq_idx(unsigned int nqueues, const str
 
 	if (ISSET(m->m_pkthdr.csum_flags, M_FLOWID))
 		flow = m->m_pkthdr.ph_flowid;
+	else
+		flow = ifq_pkt_hash(m);
 
 	return (flow % nqueues);
 }