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authorPaolo Abeni <pabeni@redhat.com>2019-03-22 16:01:56 +0100
committerDaniel Thompson <daniel@redfelineninja.org.uk>2019-09-17 16:03:05 +0100
commitb47e1a3850d394084586ffe5b4efdb6750ababae (patch)
tree37ae0ce14e5e5016667d4f123c24b619c2e77ebe
parentd985bd47619d1a6bf4a7f396820105fb6ca0e7d3 (diff)
downloadlinux-b47e1a3850d394084586ffe5b4efdb6750ababae.tar.gz
net: dev: introduce support for sch BYPASS for lockless qdisc
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>
-rw-r--r--net/core/dev.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index 13a82744a00a..08a809cf17aa 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3447,6 +3447,15 @@ 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);