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authorPaolo Abeni <pabeni@redhat.com>2019-03-22 16:01:55 +0100
committerDavid S. Miller <davem@davemloft.net>2019-03-23 21:52:36 -0400
commit28cff537ef2eed9307bc7e4e40745075637bec56 (patch)
tree19e12fe1c09bd817cae2410b5dd0b68ff6c21e43
parenttcp: add documentation for tcp_ca_state (diff)
downloadlinux-dev-28cff537ef2eed9307bc7e4e40745075637bec56.tar.xz
linux-dev-28cff537ef2eed9307bc7e4e40745075637bec56.zip
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 31284c078d06..e227475e78ca 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -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;
}
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index a117d9260558..81356ef38d1d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -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);