[PATCH net-next 1/3] net: sched: avoid unnecessary seqcount operation for lockless qdisc

Yunsheng Lin
2021-05-28T02:50:10Z

qdisc->running seqcount operation is mainly used to do heuristic
locking on q->busylock for locked qdisc, see qdisc_is_running()
and __dev_xmit_skb().

So avoid doing seqcount operation for qdisc with TCQ_F_NOLOCK
flag.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
---
include/net/sch_generic.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 1e62551..3ed6bcc 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -188,6 +188,7 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)

nolock_empty:
WRITE_ONCE(qdisc->empty, false);
+ return true;
} else if (qdisc_is_running(qdisc)) {
return false;
}
@@ -201,7 +202,6 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)

static inline void qdisc_run_end(struct Qdisc *qdisc)
{
- write_seqcount_end(&qdisc->running);
if (qdisc->flags & TCQ_F_NOLOCK) {
spin_unlock(&qdisc->seqlock);

@@ -210,6 +210,8 @@ static inline void qdisc_run_end(struct Qdisc *qdisc)
clear_bit(__QDISC_STATE_MISSED, &qdisc->state);
__netif_schedule(qdisc);
}
+ } else {
+ write_seqcount_end(&qdisc->running);
}
}

--
2.7.4