With commit c5ad119fb6c0 ("net: sched: pfifo_fast use skb_array")
pfifo_fast no longer benefit from the TCQ_F_CAN_BYPASS optimization.
Due to retpolines the cost of the enqueue()/dequeue() pair has become
relevant and we observe measurable regression for the uncontended
scenario when the packet-rate is below line rate.
After commit 46b1c18f9deb ("net: sched: put back q.qlen into a
single location") we can check for empty qdisc with a reasonably
fast operation even for nolock qdiscs.
This change extends TCQ_F_CAN_BYPASS support to nolock qdisc.
The new chunk of code mirrors closely the existing one for traditional
qdisc, leveraging a newly introduced helper to read atomically the
qdisc length.
Tested with pktgen in queue xmit mode, with pfifo_fast, a MQ
device, and MQ root qdisc:
threads vanilla patched
kpps kpps
1 2465 2889
2 4304 5188
4 7898 9589
Same as above, but with a single queue device:
threads vanilla patched
kpps kpps
1 2556 2827
2 2900 2900
4 5000 5000
8 4700 4700
No mesaurable changes in the contended scenarios, and more 10%
improvement in the uncontended ones.
Signed-off-by: Paolo Abeni <pab...@redhat.com>
Tested-by: Ivan Vecera <ivec...@redhat.com>
---
net/core/dev.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/net/core/dev.c b/net/core/dev.c
index 2b67f2aa59dd..9a6d3617f03a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3468,6 +3468,15 @@ static inline int __dev_xmit_skb(struct sk_buff *skb,
struct Qdisc *q,
if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
__qdisc_drop(skb, &to_free);
rc = NET_XMIT_DROP;
+ } else if ((q->flags & TCQ_F_CAN_BYPASS) && !q->not_empty &&
+ qdisc_run_begin(q)) {
+ qdisc_bstats_cpu_update(q, skb);
+
+ if (sch_direct_xmit(skb, q, dev, txq, NULL, true))
+ __qdisc_run(q);
+
+ qdisc_run_end(q);
+ rc = NET_XMIT_SUCCESS;
} else {
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
qdisc_run(q);
--
2.20.1
