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authorPaolo Abeni <pabeni@redhat.com>2019-03-22 16:01:55 +0100
committerDaniel Thompson <daniel@redfelineninja.org.uk>2019-09-17 16:03:05 +0100
commitd985bd47619d1a6bf4a7f396820105fb6ca0e7d3 (patch)
tree6f0845e0155afd57a91366964cb3f2df4d97051c
parentcb2441a0d4ed4ef05f21d39892bbdbf91c2e83bb (diff)
downloadlinux-d985bd47619d1a6bf4a7f396820105fb6ca0e7d3.tar.gz
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: Paolo Abeni <pabeni@redhat.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Ivan Vecera <ivecera@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/sch_generic.h11
-rw-r--r--net/sched/sch_generic.c3
2 files changed, 14 insertions, 0 deletions
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d60dfe374728..fa28bddfba47 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -108,6 +108,9 @@ struct Qdisc {
spinlock_t busylock ____cacheline_aligned_in_smp;
spinlock_t seqlock;
+
+ /* for NOLOCK qdisc, true if there are no enqueued skbs */
+ bool empty;
};
static inline void qdisc_refcount_inc(struct Qdisc *qdisc)
@@ -124,11 +127,19 @@ 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;
}
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 886a298445ce..6e46ebc995d0 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -666,6 +666,8 @@ 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;
@@ -875,6 +877,7 @@ 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);