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authorEric Dumazet <edumazet@google.com>2016-05-24 00:24:56 +0300
committerDavid S. Miller <davem@davemloft.net>2016-05-25 00:49:14 +0300
commita9efad8b24bd22616f6c749a6c029957dc76542b (patch)
tree20ab7182ee4b4fef2afebd14c960c0a3d9920c56
parent3275c0c6c522ab04afa14f80efdac6213c3883d6 (diff)
downloadlinux-a9efad8b24bd22616f6c749a6c029957dc76542b.tar.xz
net_sched: avoid too many hrtimer_start() calls
I found a serious performance bug in packet schedulers using hrtimers. sch_htb and sch_fq are definitely impacted by this problem. We constantly rearm high resolution timers if some packets are throttled in one (or more) class, and other packets are flying through qdisc on another (non throttled) class. hrtimer_start() does not have the mod_timer() trick of doing nothing if expires value does not change : if (timer_pending(timer) && timer->expires == expires) return 1; This issue is particularly visible when multiple cpus can queue/dequeue packets on the same qdisc, as hrtimer code has to lock a remote base. I used following fix : 1) Change htb to use qdisc_watchdog_schedule_ns() instead of open-coding it. 2) Cache watchdog prior expiration. hrtimer might provide this, but I prefer to not rely on some hrtimer internal. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/pkt_sched.h1
-rw-r--r--net/sched/sch_api.c4
-rw-r--r--net/sched/sch_htb.c13
3 files changed, 8 insertions, 10 deletions
diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index 401038d2f9b8..fea53f4d92ca 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -61,6 +61,7 @@ psched_tdiff_bounded(psched_time_t tv1, psched_time_t tv2, psched_time_t bound)
}
struct qdisc_watchdog {
+ u64 last_expires;
struct hrtimer timer;
struct Qdisc *qdisc;
};
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 64f71a2155f3..ddf047df5361 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -607,6 +607,10 @@ void qdisc_watchdog_schedule_ns(struct qdisc_watchdog *wd, u64 expires, bool thr
if (throttle)
qdisc_throttled(wd->qdisc);
+ if (wd->last_expires == expires)
+ return;
+
+ wd->last_expires = expires;
hrtimer_start(&wd->timer,
ns_to_ktime(expires),
HRTIMER_MODE_ABS_PINNED);
diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index f6bf5818ed4d..d4b4218af6b1 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -928,17 +928,10 @@ ok:
}
}
qdisc_qstats_overlimit(sch);
- if (likely(next_event > q->now)) {
- if (!test_bit(__QDISC_STATE_DEACTIVATED,
- &qdisc_root_sleeping(q->watchdog.qdisc)->state)) {
- ktime_t time = ns_to_ktime(next_event);
- qdisc_throttled(q->watchdog.qdisc);
- hrtimer_start(&q->watchdog.timer, time,
- HRTIMER_MODE_ABS_PINNED);
- }
- } else {
+ if (likely(next_event > q->now))
+ qdisc_watchdog_schedule_ns(&q->watchdog, next_event, true);
+ else
schedule_work(&q->work);
- }
fin:
return skb;
}