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Commit 12efa1fa authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net_sched: gen_estimator: account for timer drifts 



Under heavy stress, timer used in estimators tend to slowly be delayed
by a few jiffies, leading to inaccuracies.

Lets remember what was the last scheduled jiffies so that we get more
precise estimations, without having to add a multiply/divide in the loop
to account for the drifts.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e01b16a7

net/core/gen_estimator.c

+16 −9
Original line number Diff line number Diff line
@@ -78,8 +78,7 @@ 


#define EST_MAX_INTERVAL	5



struct gen_estimator

{

struct gen_estimator {

	struct list_head	list;

	struct gnet_stats_basic_packed	*bstats;

	struct gnet_stats_rate_est64	*rate_est;
@@ -96,8 +95,8 @@ struct gen_estimator 
	struct rcu_head		head;

};



struct gen_estimator_head

{

struct gen_estimator_head {

	unsigned long		next_jiffies;

	struct timer_list	timer;

	struct list_head	list;

};
@@ -146,8 +145,15 @@ static void est_timer(unsigned long arg) 
			spin_unlock(e->stats_lock);

	}



	if (!list_empty(&elist[idx].list))

		mod_timer(&elist[idx].timer, jiffies + ((HZ/4) << idx));

	if (!list_empty(&elist[idx].list)) {

		elist[idx].next_jiffies += ((HZ/4) << idx);



		if (unlikely(time_after_eq(jiffies, elist[idx].next_jiffies))) {

			/* Ouch... timer was delayed. */

			elist[idx].next_jiffies = jiffies + 1;

		}

		mod_timer(&elist[idx].timer, elist[idx].next_jiffies);

	}

	rcu_read_unlock();

}
@@ -251,9 +257,10 @@ int gen_new_estimator(struct gnet_stats_basic_packed *bstats, 
		setup_timer(&elist[idx].timer, est_timer, idx);

	}



	if (list_empty(&elist[idx].list))

		mod_timer(&elist[idx].timer, jiffies + ((HZ/4) << idx));



	if (list_empty(&elist[idx].list)) {

		elist[idx].next_jiffies = jiffies + ((HZ/4) << idx);

		mod_timer(&elist[idx].timer, elist[idx].next_jiffies);

	}

	list_add_rcu(&est->list, &elist[idx].list);

	gen_add_node(est);

	spin_unlock_bh(&est_tree_lock);