tcp: Use jenkins_hash32() in hostcache

As other parts of the base tcp stack (eg.
tcp fastopen) already use jenkins_hash32,
and the properties appear reasonably good,
switching to use that.

Reviewed By: tuexen, #transport, ae
MFC after: 2 weeks
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29515

share/man/man4/tcp.4

@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd February 13, 2021
+.Dd April 8, 2021
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -628,7 +628,6 @@ Defaults to 60 seconds.
 Enable support for TCP Explicit Congestion Notification (ECN).
 ECN allows a TCP sender to reduce the transmission rate in order to
 avoid packet drops.
-Settings:
 .Bl -tag -compact
 .It 0
 Disable ECN.
@@ -638,6 +637,7 @@ Outgoing connections will request ECN.
 .It 2
 Allow incoming connections to request ECN.
 Outgoing connections will not request ECN.
+(default)
 .El
 .It Va ecn.maxretries
 Number of retries (SYN or SYN/ACK retransmits) before disabling ECN on a
@@ -674,6 +674,54 @@ Enable path MTU blackhole detection only for IPv6.
 MSS to try for IPv4 if PMTU blackhole detection is turned on.
 .It Va v6pmtud_blackhole_mss
 MSS to try for IPv6 if PMTU blackhole detection is turned on.
+.It Va hostcache.enable
+The TCP host cache is used to cache connection details and metrics to
+improve future performance of connections between the same hosts.
+At the completion of a TCP connection, a host will cache information
+for the connection for some defined period of time.
+.Bl -tag -compact
+.It 0
+Disable the host cache.
+.It 1
+Enable the host cache. (default)
+.It Va hostcache.purgenow
+Immediately purge all entries once set to any value.
+Setting this to 2 will also reseed the hash salt.
+.It Va hostcache.purge
+Expire all entires on next pruning of host cache entries.
+Any non-zero setting will be reset to zero, once the pruge
+is running.
+.Bl -tag -compact
+.It 0
+Do not purge all entries when pruning the host cache. (default)
+.It 1
+Purge all entries when doing the next pruning.
+.It 2
+Purge all entries, and also reseed the hash salt.
+.It Va hostcache.prune
+Time in seconds between pruning expired host cache entries.
+Defaults to 300 (5 minutes).
+.It Va hostcache.expire
+Time in seconds, how long a entry should be kept in the
+host cache since last accessed.
+Defaults to 3600 (1 hour).
+.It Va hostcache.count
+The current number of entries in the host cache.
+.It Va hostcache.bucketlimit
+The maximum number of entries for the same hash.
+Defaults to 30.
+.It Va hostcache.hashsize
+Size of TCP hostcache hashtable.
+This number has to be a power of two, or will be rejected.
+Defaults to 512.
+.It Va hostcache.cachelimit
+Overall entry limit for hostcache.
+Defaults to hashsize * bucketlimit.
+.It Va hostcache.histo
+Provide a Histogram of the hostcache hash utilization.
+.It Va hostcache.list
+Provide a complete list of all current entries in the host
+cache.
 .It Va functions_available
 List of available TCP function blocks (TCP stacks).
 .It Va functions_default

sys/netinet/tcp_hostcache.c

@@ -71,6 +71,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/systm.h>
+#include <sys/hash.h>
 #include <sys/jail.h>
 #include <sys/kernel.h>
 #include <sys/lock.h>
@@ -127,6 +128,7 @@ struct tcp_hostcache {
 	uma_zone_t	zone;
 	u_int		hashsize;
 	u_int		hashmask;
+	u_int		hashsalt;
 	u_int		bucket_limit;
 	u_int		cache_count;
 	u_int		cache_limit;
@@ -210,16 +212,14 @@ SYSCTL_PROC(_net_inet_tcp_hostcache, OID_AUTO, purgenow,
 
 static MALLOC_DEFINE(M_HOSTCACHE, "hostcache", "TCP hostcache");
 
+/* Use jenkins_hash32(), as in other parts of the tcp stack */
 #define HOSTCACHE_HASH(ip) \
-	(((ip)->s_addr ^ ((ip)->s_addr >> 7) ^ ((ip)->s_addr >> 17)) &	\
+	(jenkins_hash32((uint32_t *)(ip), 1, V_tcp_hostcache.hashsalt) & \
-	  V_tcp_hostcache.hashmask)
+	 V_tcp_hostcache.hashmask)
 
-/* XXX: What is the recommended hash to get good entropy for IPv6 addresses? */
 #define HOSTCACHE_HASH6(ip6)				\
-	(((ip6)->s6_addr32[0] ^				\
+	(jenkins_hash32((uint32_t *)&((ip6)->s6_addr32[0]), 4, \
-	  (ip6)->s6_addr32[1] ^				\
+	 V_tcp_hostcache.hashsalt) & \
-	  (ip6)->s6_addr32[2] ^				\
-	  (ip6)->s6_addr32[3]) &			\
 	 V_tcp_hostcache.hashmask)
 
 #define THC_LOCK(lp)		mtx_lock(lp)
@@ -239,6 +239,7 @@ tcp_hc_init(void)
 	V_tcp_hostcache.bucket_limit = TCP_HOSTCACHE_BUCKETLIMIT;
 	V_tcp_hostcache.expire = TCP_HOSTCACHE_EXPIRE;
 	V_tcp_hostcache.prune = TCP_HOSTCACHE_PRUNE;
+	V_tcp_hostcache.hashsalt = arc4random();
 
 	TUNABLE_INT_FETCH("net.inet.tcp.hostcache.hashsize",
 	    &V_tcp_hostcache.hashsize);
@@ -836,6 +837,8 @@ tcp_hc_purge(void *arg)
 	int all = 0;
 
 	if (V_tcp_hostcache.purgeall) {
+		if (V_tcp_hostcache.purgeall == 2)
+			V_tcp_hostcache.hashsalt = arc4random();
 		all = 1;
 		V_tcp_hostcache.purgeall = 0;
 	}
@@ -860,6 +863,8 @@ sysctl_tcp_hc_purgenow(SYSCTL_HANDLER_ARGS)
 	if (error || !req->newptr)
 		return (error);
 
+	if (val == 2)
+		V_tcp_hostcache.hashsalt = arc4random();
 	tcp_hc_purge_internal(1);
 
 	callout_reset(&V_tcp_hc_callout, V_tcp_hostcache.prune * hz,