From: Paolo Abeni <pabeni@redhat.com>
Date: Fri, 22 Mar 2019 16:01:56 +0100
Subject: net: dev: introduce support for sch BYPASS for lockless qdisc
Patch-mainline: v5.2-rc1
Git-commit: ba27b4cdaaa66561aaedb2101876e563738d36fe
References: bsc#1183405
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.
v1 -> v2:
- rebased after flag name change
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Ivan Vecera <ivecera@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>
Acked-by: Michal Kubecek <mkubecek@suse.cz>
---
net/core/dev.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3422,6 +3422,15 @@ 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->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);