Now, virtio-net already supports per-queue moderation parameter
setting. Based on this, we use the linux dimlib to support
dynamic coalescing moderation for virtio-net.

Due to some scheduling issues, we only support and test the rx dim.

Some test results:

I. Sockperf UDP
=================================================
1. Env
rxq_0 with affinity to cpu_0.

2. Cmd
client: taskset -c 0 sockperf tp -p 8989 -i $IP -t 10 -m 16B
server: taskset -c 0 sockperf sr -p 8989

3. Result
dim off: 1143277.00 rxpps, throughput 17.844 MBps, cpu is 100%.
dim on:  1124161.00 rxpps, throughput 17.610 MBps, cpu is 83.5%.
=================================================


II. Redis
=================================================
1. Env
There are 8 rxqs, and rxq_i with affinity to cpu_i.

2. Result
When all cpus are 100%, ops/sec of memtier_benchmark client is
dim off:  978437.23
dim on:  1143638.28
=================================================


III. Nginx
=================================================
1. Env
There are 8 rxqs and rxq_i with affinity to cpu_i.

2. Result
When all cpus are 100%, requests/sec of wrk client is
dim off:  877931.67
dim on:  1019160.31
=================================================

IV. Latency of sockperf udp
=================================================
1. Rx cmd
taskset -c 0 sockperf sr -p 8989

2. Tx cmd
taskset -c 0 sockperf pp -i ${ip} -p 8989 -t 10

After running this cmd 5 times and averaging the results,

3. Result
dim off: 17.7735 usec
dim on:  18.0110 usec
=================================================

Changelog:
v1->v2:
- Patch(2/5): a minor fix.
- Patch(4/5):
   - improved the judgment of dim switch conditions.
   - fix safe problem of work thread.
- Patch(5/5): Drop the tx dim implementation.

Heng Qi (5):
  virtio-net: returns whether napi is complete
  virtio-net: separate rx/tx coalescing moderation cmds
  virtio-net: extract virtqueue coalescig cmd for reuse
  virtio-net: support rx netdim
  virtio-net: return -EOPNOTSUPP for adaptive-tx

 drivers/net/virtio_net.c | 331 ++++++++++++++++++++++++++++++++-------
 1 file changed, 274 insertions(+), 57 deletions(-)

-- 
2.19.1.6.gb485710b