live migration's performance with compression enabled is much worse than compression disabled
Description of problem:

Steps to reproduce:
1. Run QEMU the Guests with 1Gpbs network on source host and destination host with QEMU command line
2. Run some memory work loads on Guest, for example, ./memtester 1G 1
3. Set migration parameters in QEMU monitor. On source and destination, 
   execute: #migrate_set_capability compress on
   Other compression parameters are all default. 
4. Run migrate command, # migrate -d tcp:10.156.208.154:4000
5. The results: 
   - without compression：  total time:  197366 ms   throughput:   937.81 mbps  transferred Ram: 22593703 kbytes 
   - with compression: total time:  281711 ms   throughput:  90.24 mbps    transferred Ram: 3102898 kbytes  

When compression is enabled, the compression transferred ram is reduced a lot. But the throughput is down badly.
The total time of live migration with compression is longer than without compression. 
I tried with 100G network bandwidth, it also has the same problem.
Additional information: