From: Eric Dumazet <eric.duma...@gmail.com> Date: Sat, 04 Jun 2016 20:02:28 -0700
> From: Eric Dumazet <eduma...@google.com> > > Note: Tom Herbert posted almost same patch 3 months back, but for > different reasons. > > The reasons we want to get rid of this spin_trylock() are : > > 1) Under high qdisc pressure, the spin_trylock() has almost no > chance to succeed. > > 2) We loop multiple times in softirq handler, eventually reaching > the max retry count (10), and we schedule ksoftirqd. > > Since we want to adhere more strictly to ksoftirqd being waked up in > the future (https://lwn.net/Articles/687617/), better avoid spurious > wakeups. > > 3) calls to __netif_reschedule() dirty the cache line containing > q->next_sched, slowing down the owner of qdisc. > > 4) RT kernels can not use the spin_trylock() here. > > With help of busylock, we get the qdisc spinlock fast enough, and > the trylock trick brings only performance penalty. > > Depending on qdisc setup, I observed a gain of up to 19 % in qdisc > performance (1016600 pps instead of 853400 pps, using prio+tbf+fq_codel) > > ("mpstat -I SCPU 1" is much happier now) > > Signed-off-by: Eric Dumazet <eduma...@google.com> Applied, thanks.
