net_sched: htb: do not setup default rate estimators

With a thousand htb classes, est_timer() spends ~5 million cpu cycles
and throws out cpu cache, because each htb class has a default
rate estimator (est 4sec 16sec).

Most users do not use default rate estimators, so switch htb
to not setup ones.

Add a module parameter (htb_rate_est) so that users relying
on this default rate estimator can revert the behavior.

echo 1 >/sys/module/sch_htb/parameters/htb_rate_est
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -65,6 +65,10 @@ static int htb_hysteresis __read_mostly = 0; /* whether to use mode hysteresis f
 module_param    (htb_hysteresis, int, 0640);
 MODULE_PARM_DESC(htb_hysteresis, "Hysteresis mode, less CPU load, less accurate");
 
+static int htb_rate_est = 0; /* htb classes have a default rate estimator */
+module_param(htb_rate_est, int, 0640);
+MODULE_PARM_DESC(htb_rate_est, "setup a default rate estimator (4sec 16sec) for htb classes");
+
 /* used internaly to keep status of single class */
 enum htb_cmode {
 	HTB_CANT_SEND,		/* class can't send and can't borrow */
@@ -1366,6 +1370,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 		if (!cl)
 			goto failure;
 
+		if (htb_rate_est || tca[TCA_RATE]) {
 			err = gen_new_estimator(&cl->bstats, &cl->rate_est,
 						qdisc_root_sleeping_lock(sch),
 						tca[TCA_RATE] ? : &est.nla);
@@ -1373,6 +1378,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 				kfree(cl);
 				goto failure;
 			}
+		}
 
 		cl->refcnt = 1;
 		cl->children = 0;