Merge branch 'tcp-tsq-perf'

Merge branch 'tcp-tsq-perf'

Eric Dumazet says:

====================
tcp: tsq: performance series

Under very high TX stress, CPU handling NIC TX completions can spend
considerable amount of cycles handling TSQ (TCP Small Queues) logic.

This patch series avoids some atomic operations, but most notable
patch is the 3rd one, allowing other cpus processing ACK packets and
calling tcp_write_xmit() to grab TCP_TSQ_DEFERRED so that
tcp_tasklet_func() can skip already processed sockets.

This avoid lots of lock acquisitions and cache lines accesses,
particularly under load.

In v2, I added :

- tcp_small_queue_check() change to allow 1st and 2nd packets
  in write queue to be sent, even in the case TX completion of
    already acknowledged packets did not happen yet.
      This helps when TX completion coalescing parameters are set
        even to insane values, and/or busy polling is used.

- A reorganization of struct sock fields to
  lower false sharing and increase data locality.

- Then I moved tsq_flags from tcp_sock to struct sock also
  to reduce cache line misses during TX completions.

I measured an overall throughput gain of 22 % for heavy TCP use
over a single TX queue.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>