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H A Dpktgen.cdiff baac167b706600ebe7158acaeb7c489ae9d0bb8b Thu Jun 26 06:16:49 CDT 2014 Jesper Dangaard Brouer <brouer@redhat.com> pktgen: avoid expensive set_current_state() call in loop

Avoid calling set_current_state() inside the busy-loop in
pktgen_thread_worker(). In case of pkt_dev->delay, then it is still
used/enabled in pktgen_xmit() via the spin() call.

The set_current_state(TASK_INTERRUPTIBLE) uses a xchg, which implicit
is LOCK prefixed. I've measured the asm LOCK operation to take approx
8ns on this E5-2630 CPU. Performance increase corrolate with this
measurement.

Performance data with CLONE_SKB==100000, rx-usecs=30:
(single CPU performance, ixgbe 10Gbit/s, E5-2630)
* Prev: 5454050 pps --> 183.35ns (1/5454050*10^9)
* Now: 5684009 pps --> 175.93ns (1/5684009*10^9)
* Diff: +229959 pps --> -7.42ns

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>