netdev - [PATCH net-next 0/2] net: dev: BYPASS for lockless qdisc

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Date:   Thu, 21 Mar 2019 11:14:17 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Ivan Vecera <ivecera@...hat.com>
Subject: [PATCH net-next 0/2] net: dev: BYPASS for lockless qdisc

This patch series is aimed at improving xmit performances of lockless qdisc
in the uncontended scenario.

After the lockless refactor pfifo_fast can't leverage the BYPASS optimization.
Due to retpolines the overhead for the avoidables enqueue and dequeue operations
has increased and we see measurable regressions.

The first patch introduces and maintains an additional flag inside the qdisc
struct, tracking the queue status (empty/not empty) and the second patch uses
such info to implement the BYPASS code path for lockless qdisc.
Overall this avoids up to 2 indirect calls per xmit packet when the packet
rate is below line rate.
Detailed performance figures are reported in the 2nd patch.

Paolo Abeni (2):
  net: sched: add empty status flag for NOLOCK qdisc
  net: dev: introduce support for sch BYPASS for lockless qdisc

 include/net/sch_generic.h | 17 +++++++++++++++++
 net/core/dev.c            |  9 +++++++++
 net/sched/sch_generic.c   |  2 ++
 3 files changed, 28 insertions(+)

-- 
2.20.1