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tcp: Use jenkins_hash32() in hostcache

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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
This commit is contained in:
Richard Scheffenegger 2021-04-08 20:28:43 +02:00
parent 373ffc62c1
commit b878ec024b
2 changed files with 62 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
share/man/man4/tcp.4
View File

@ -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

19
sys/netinet/tcp_hostcache.c
View File

@ -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)) & \
V_tcp_hostcache.hashmask)
(jenkins_hash32((uint32_t *)(ip), 1, V_tcp_hostcache.hashsalt) & \
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] ^ \
(ip6)->s6_addr32[1] ^ \
(ip6)->s6_addr32[2] ^ \
(ip6)->s6_addr32[3]) & \
(jenkins_hash32((uint32_t *)&((ip6)->s6_addr32[0]), 4, \
V_tcp_hostcache.hashsalt) & \
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,