* [PATCH net-next] net_sched: gen_estimator: account for timer drifts
@ 2016-12-02 16:11 Eric Dumazet
2016-12-03 21:12 ` David Miller
0 siblings, 1 reply; 3+ messages in thread
From: Eric Dumazet @ 2016-12-02 16:11 UTC (permalink / raw)
To: David Miller; +Cc: netdev
From: Eric Dumazet <edumazet@google.com>
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>
---
net/core/gen_estimator.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
index cad8e791f28e..0993844faeea 100644
--- a/net/core/gen_estimator.c
+++ b/net/core/gen_estimator.c
@@ -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);
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH net-next] net_sched: gen_estimator: account for timer drifts
2016-12-02 16:11 [PATCH net-next] net_sched: gen_estimator: account for timer drifts Eric Dumazet
@ 2016-12-03 21:12 ` David Miller
2016-12-03 21:54 ` Eric Dumazet
0 siblings, 1 reply; 3+ messages in thread
From: David Miller @ 2016-12-03 21:12 UTC (permalink / raw)
To: eric.dumazet; +Cc: netdev
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 02 Dec 2016 08:11:00 -0800
> From: Eric Dumazet <edumazet@google.com>
>
> 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>
Applied.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH net-next] net_sched: gen_estimator: account for timer drifts
2016-12-03 21:12 ` David Miller
@ 2016-12-03 21:54 ` Eric Dumazet
0 siblings, 0 replies; 3+ messages in thread
From: Eric Dumazet @ 2016-12-03 21:54 UTC (permalink / raw)
To: David Miller; +Cc: netdev
On Sat, 2016-12-03 at 16:12 -0500, David Miller wrote:
> Applied.
Thanks David.
I also have to get rid of the WRITE_ONCE() done in est_timer(), since it
does not work properly on 32bit kernels.
It will target net-next, since it is not a very serious problem.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-12-02 16:11 [PATCH net-next] net_sched: gen_estimator: account for timer drifts Eric Dumazet
2016-12-03 21:12 ` David Miller
2016-12-03 21:54 ` Eric Dumazet
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