Author: alfred
Date: Tue Nov 27 03:04:24 2012
New Revision: 243594
URL: http://svnweb.freebsd.org/changeset/base/243594
Log:
Auto size the tcbhashsize structure based on max sockets.
While here, also make the code that enforces power-of-two more
forgiving, instead of just resetting to 512, graciously round-down
to the next lower power of two.
Modified:
head/sys/netinet/tcp_subr.c
Modified: head/sys/netinet/tcp_subr.c
==============================================================================
--- head/sys/netinet/tcp_subr.c Tue Nov 27 02:28:42 2012 (r243593)
+++ head/sys/netinet/tcp_subr.c Tue Nov 27 03:04:24 2012 (r243594)
@@ -235,7 +235,7 @@ static char * tcp_log_addr(struct in_con
* variable net.inet.tcp.tcbhashsize
*/
#ifndef TCBHASHSIZE
-#define TCBHASHSIZE 512
+#define TCBHASHSIZE 0
#endif
/*
@@ -282,11 +282,35 @@ tcp_inpcb_init(void *mem, int size, int
return (0);
}
+/*
+ * Take a value and get the next power of 2 that doesn't overflow.
+ * Used to size the tcp_inpcb hash buckets.
+ */
+static int
+maketcp_hashsize(int size)
+{
+ int hashsize;
+
+ /*
+ * auto tune.
+ * get the next power of 2 higher than maxsockets.
+ */
+ hashsize = 1 << fls(size);
+ /* catch overflow, and just go one power of 2 smaller */
+ if (hashsize < size) {
+ hashsize = 1 << (fls(size) - 1);
+ }
+ return (hashsize);
+}
+
void
tcp_init(void)
{
+ const char *tcbhash_tuneable;
int hashsize;
+ tcbhash_tuneable = "net.inet.tcp.tcbhashsize";
+
if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN,
&V_tcp_hhh[HHOOK_TCP_EST_IN], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
printf("%s: WARNING: unable to register helper hook\n",
__func__);
@@ -295,10 +319,43 @@ tcp_init(void)
printf("%s: WARNING: unable to register helper hook\n",
__func__);
hashsize = TCBHASHSIZE;
- TUNABLE_INT_FETCH("net.inet.tcp.tcbhashsize", &hashsize);
+ TUNABLE_INT_FETCH(tcbhash_tuneable, &hashsize);
+ if (hashsize == 0) {
+ /*
+ * Auto tune the hash size based on maxsockets.
+ * A perfect hash would have a 1:1 mapping
+ * (hashsize = maxsockets) however it's been
+ * suggested that O(2) average is better.
+ */
+ hashsize = maketcp_hashsize(maxsockets / 4);
+ /*
+ * Our historical default is 512,
+ * do not autotune lower than this.
+ */
+ if (hashsize < 512)
+ hashsize = 512;
+ if (bootverbose)
+ printf("%s: %s auto tuned to %d\n", __func__,
+ tcbhash_tuneable, hashsize);
+ }
+ /*
+ * We require a hashsize to be a power of two.
+ * Previously if it was not a power of two we would just reset it
+ * back to 512, which could be a nasty surprise if you did not notice
+ * the error message.
+ * Instead what we do is clip it to the closest power of two lower
+ * than the specified hash value.
+ */
if (!powerof2(hashsize)) {
- printf("WARNING: TCB hash size not a power of 2\n");
- hashsize = 512; /* safe default */
+ int oldhashsize = hashsize;
+
+ hashsize = maketcp_hashsize(hashsize);
+ /* prevent absurdly low value */
+ if (hashsize < 16)
+ hashsize = 16;
+ printf("%s: WARNING: TCB hash size not a power of 2, "
+ "clipped from %d to %d.\n", __func__, oldhashsize,
+ hashsize);
}
in_pcbinfo_init(&V_tcbinfo, "tcp", &V_tcb, hashsize, hashsize,
"tcp_inpcb", tcp_inpcb_init, NULL, UMA_ZONE_NOFREE,
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