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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: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2016-12-02 08:11:00 -08:00 committed by David S. Miller
parent e01b16a7e2
commit 12efa1fa43
1 changed files with 16 additions and 9 deletions
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25
net/core/gen_estimator.c
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@ -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 @@ skip:
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);