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Auto size the tcbhashsize structure based on max sockets.

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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.
This commit is contained in:
Alfred Perlstein 2012-11-27 03:04:24 +00:00
parent 5466211d6d
commit 08373e0bc4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=243594
1 changed files with 61 additions and 4 deletions
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65
sys/netinet/tcp_subr.c
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@ -235,7 +235,7 @@ static char * tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th,
* 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 flags)
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,