On 27.11.2012 04:04, Alfred Perlstein wrote:
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.
The porthash (also a parameter to in_pcbinfo_init()) should not be
scaled the same as tcbhashsize. It's unlikely that anyone is going
to have more than a thousand listen ports.
The default tcbhashsize scaling factor of maxsockets / 4 is IMHO
excessive. If someone is running at the limit he's going to up
maxsockets to double the target load. Dividing by 8 is a better
balance for normal and well used large memory machines.
The hashsize calculation logic is done a bit in a roundabout way.
What do think of the attached patch to fix the porthash and to simplify
the hashsize logic?
--
Andre
Index: netinet/tcp_subr.c
===================================================================
--- netinet/tcp_subr.c (revision 243631)
+++ netinet/tcp_subr.c (working copy)
@@ -229,14 +229,17 @@
void *ip4hdr, const void *ip6hdr);
/*
- * Target size of TCP PCB hash tables. Must be a power of two.
+ * Minimal size of TCP PCB hash tables. Must be a power of two.
*
* Note that this can be overridden by the kernel environment
* variable net.inet.tcp.tcbhashsize
*/
-#ifndef TCBHASHSIZE
-#define TCBHASHSIZE 0
+#ifndef TCBMINHASHSIZE
+#define TCBMINHASHSIZE 512
#endif
+#ifndef TCBPORTHASHSIZE
+#define TCBPORTHASHSIZE 512
+#endif
/*
* XXX
@@ -282,35 +285,10 @@
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__);
@@ -318,49 +296,17 @@
&V_tcp_hhh[HHOOK_TCP_EST_OUT], HHOOK_NOWAIT|HHOOK_HEADISINVNET) !=
0)
printf("%s: WARNING: unable to register helper hook\n",
__func__);
- hashsize = TCBHASHSIZE;
- 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);
+ tcp_tcbhashsize = 0x1 << fls((maxsockets / 8) - 1);
+ TUNABLE_INT_FETCH("net.inet.tcp.tcbhashsize", &tcp_tcbhashsize);
+ if (!powerof2(tcp_tcbhashsize) ||
+ tcp_tcbhashsize < TCBMINHASHSIZE) {
+ printf("WARNING: TCB hash size not a power of 2 or too
small\n");
+ tcp_tcbhashsize = TCBMINHASHSIZE;
}
- /*
- * 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)) {
- int oldhashsize = hashsize;
+ in_pcbinfo_init(&V_tcbinfo, "tcp", &V_tcb, tcp_tcbhashsize,
+ TCBPORTHASHSIZE, "tcp_inpcb", tcp_inpcb_init, NULL,
+ UMA_ZONE_NOFREE, IPI_HASHFIELDS_4TUPLE);
- 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,
- IPI_HASHFIELDS_4TUPLE);
-
/*
* These have to be type stable for the benefit of the timers.
*/
@@ -393,7 +339,6 @@
tcp_rexmit_min = 1;
tcp_rexmit_slop = TCPTV_CPU_VAR;
tcp_finwait2_timeout = TCPTV_FINWAIT2_TIMEOUT;
- tcp_tcbhashsize = hashsize;
TUNABLE_INT_FETCH("net.inet.tcp.soreceive_stream",
&tcp_soreceive_stream);
if (tcp_soreceive_stream) {
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