dpif-netdev: Detailed performance stats for PMDs

dpif-netdev: Detailed performance stats for PMDs

This patch instruments the dpif-netdev datapath to record detailed
statistics of what is happening in every iteration of a PMD thread.

The collection of detailed statistics can be controlled by a new
Open_vSwitch configuration parameter "other_config:pmd-perf-metrics".
By default it is disabled. The run-time overhead, when enabled, is
in the order of 1%.

The covered metrics per iteration are:
  - cycles
  - packets
  - (rx) batches
  - packets/batch
  - max. vhostuser qlen
  - upcalls
  - cycles spent in upcalls

This raw recorded data is used threefold:

1. In histograms for each of the following metrics:
   - cycles/iteration (log.)
   - packets/iteration (log.)
   - cycles/packet
   - packets/batch
   - max. vhostuser qlen (log.)
   - upcalls
   - cycles/upcall (log)
   The histograms bins are divided linear or logarithmic.

2. A cyclic history of the above statistics for 999 iterations

3. A cyclic history of the cummulative/average values per millisecond
   wall clock for the last 1000 milliseconds:
   - number of iterations
   - avg. cycles/iteration
   - packets (Kpps)
   - avg. packets/batch
   - avg. max vhost qlen
   - upcalls
   - avg. cycles/upcall

The gathered performance metrics can be printed at any time with the
new CLI command

ovs-appctl dpif-netdev/pmd-perf-show [-nh] [-it iter_len] [-ms ms_len]
    [-pmd core] [dp]

The options are

-nh:            Suppress the histograms
-it iter_len:   Display the last iter_len iteration stats
-ms ms_len:     Display the last ms_len millisecond stats
-pmd core:      Display only the specified PMD

The performance statistics are reset with the existing
dpif-netdev/pmd-stats-clear command.

The output always contains the following global PMD statistics,
similar to the pmd-stats-show command:

Time: 15:24:55.270
Measurement duration: 1.008 s

pmd thread numa_id 0 core_id 1:

  Cycles:            2419034712  (2.40 GHz)
  Iterations:            572817  (1.76 us/it)
  - idle:                486808  (15.9 % cycles)
  - busy:                 86009  (84.1 % cycles)
  Rx packets:           2399607  (2381 Kpps, 848 cycles/pkt)
  Datapath passes:      3599415  (1.50 passes/pkt)
  - EMC hits:            336472  ( 9.3 %)
  - Megaflow hits:      3262943  (90.7 %, 1.00 subtbl lookups/hit)
  - Upcalls:                  0  ( 0.0 %, 0.0 us/upcall)
  - Lost upcalls:             0  ( 0.0 %)
  Tx packets:           2399607  (2381 Kpps)
  Tx batches:            171400  (14.00 pkts/batch)

Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Acked-by: Billy O'Mahony <billy.o.mahony@intel.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>