netdev - [PATCH net-next 0/4] net: rps/rfs improvements

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Date:   Tue, 28 Mar 2023 23:50:17 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Jason Xing <kernelxing@...cent.com>, netdev@...r.kernel.org,
        eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 0/4] net: rps/rfs improvements

Jason Xing attempted to optimize napi_schedule_rps() by avoiding
unneeded NET_RX_SOFTIRQ raises: [1], [2]

This is quite complex to implement properly. I chose to implement
the idea, and added a similar optimization in ____napi_schedule()

Overall, in an intensive RPC workload, with 32 TX/RX queues with RFS
I was able to observe a ~10% reduction of NET_RX_SOFTIRQ
invocations.

While this had no impact on throughput or cpu costs on this synthetic
benchmark, we know that firing NET_RX_SOFTIRQ from softirq handler
can force __do_softirq() to wakeup ksoftirqd when need_resched() is true.
This can have a latency impact on stressed hosts.

[1] https://lore.kernel.org/lkml/20230325152417.5403-1-kerneljasonxing@gmail.com/
[2] https://lore.kernel.org/netdev/20230328142112.12493-1-kerneljasonxing@gmail.com/

Eric Dumazet (4):
  net: napi_schedule_rps() cleanup
  net: add softnet_data.in_net_rx_action
  net: optimize napi_schedule_rps()
  net: optimize ____napi_schedule() to avoid extra NET_RX_SOFTIRQ

 include/linux/netdevice.h |  1 +
 net/core/dev.c            | 46 ++++++++++++++++++++++++++++++---------
 2 files changed, 37 insertions(+), 10 deletions(-)

-- 
2.40.0.348.gf938b09366-goog