From a9efad8b24bd22616f6c749a6c029957dc76542b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 23 May 2016 14:24:56 -0700 Subject: 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 Signed-off-by: David S. Miller --- include/net/pkt_sched.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/net') 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; }; -- cgit v1.2.3