Commit 28cff537 authored by Paolo Abeni's avatar Paolo Abeni Committed by David S. Miller
Browse files

net: sched: add empty status flag for NOLOCK qdisc 



The queue is marked not empty after acquiring the seqlock,
and it's up to the NOLOCK qdisc clearing such flag on dequeue.
Since the empty status lays on the same cache-line of the
seqlock, it's always hot on cache during the updates.

This makes the empty flag update a little bit loosy. Given
the lack of synchronization between enqueue and dequeue, this
is unavoidable.

v2 -> v3:
 - qdisc_is_empty() has a const argument (Eric)

v1 -> v2:
 - use really an 'empty' flag instead of 'not_empty', as
   suggested by Eric

Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarIvan Vecera <ivecera@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 576fd2f7

include/net/sch_generic.h

+11 −0
Original line number Diff line number Diff line
@@ -113,6 +113,9 @@ struct Qdisc { 


	spinlock_t		busylock ____cacheline_aligned_in_smp;

	spinlock_t		seqlock;



	/* for NOLOCK qdisc, true if there are no enqueued skbs */

	bool			empty;

	struct rcu_head		rcu;

};
@@ -143,11 +146,19 @@ static inline bool qdisc_is_running(struct Qdisc *qdisc) 
	return (raw_read_seqcount(&qdisc->running) & 1) ? true : false;

}



static inline bool qdisc_is_empty(const struct Qdisc *qdisc)

{

	if (qdisc->flags & TCQ_F_NOLOCK)

		return qdisc->empty;

	return !qdisc->q.qlen;

}



static inline bool qdisc_run_begin(struct Qdisc *qdisc)

{

	if (qdisc->flags & TCQ_F_NOLOCK) {

		if (!spin_trylock(&qdisc->seqlock))

			return false;

		qdisc->empty = false;

	} else if (qdisc_is_running(qdisc)) {

		return false;

	}

net/sched/sch_generic.c

+3 −0
Original line number Diff line number Diff line
@@ -671,6 +671,8 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) 
		qdisc_qstats_cpu_backlog_dec(qdisc, skb);

		qdisc_bstats_cpu_update(qdisc, skb);

		qdisc_qstats_atomic_qlen_dec(qdisc);

	} else {

		qdisc->empty = true;

	}



	return skb;
@@ -880,6 +882,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue, 
	sch->enqueue = ops->enqueue;

	sch->dequeue = ops->dequeue;

	sch->dev_queue = dev_queue;

	sch->empty = true;

	dev_hold(dev);

	refcount_set(&sch->refcnt, 1);

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