Code review comment for lp:~gl-az/percona-xtrabackup/xb-2.1-lp1160788-decrypt-decompress

Some metrics from HP Clout instance:

$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 1
Core(s) per socket: 1
CPU socket(s): 2
NUMA node(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 2
Stepping: 3
CPU MHz: 2666.760
BogoMIPS: 5333.52
Hypervisor vendor: KVM
Virtualization type: full
L1d cache: 32K
L1i cache: 32K
L2 cache: 4096K
NUMA node0 CPU(s): 0,1

Database was prepped with sysbench parallel-prepare, 16 tables and 5000000 rows for about ~20GB.

Backup was performed with --compress --encrypt=AES256

Serial, no parallel decrypt/decompress:
  $time innobackupex --decrypt=AES256 --encrypt-key=12345678123456781234567812345678 --decompress ./backup

  real 10m50.492s
  user 9m51.688s
  sys 0m53.628s

Parallel with 2 forks decrypt/decompress:
  $time innobackupex --decrypt=AES256 --encrypt-key=12345678123456781234567812345678 --decompress --parallel=2 ./backup

  real 5m38.778s
  user 9m50.381s
  sys 0m56.072s

Parallel with 4 forks decrypt/decompress:
  $time innobackupex --decrypt=AES256 --encrypt-key=12345678123456781234567812345678 --decompress --parallel=4 ./backup

  real 5m38.861s
  user 9m50.900s
  sys 0m56.473s

So we see a linear improvement here with CPU availability as long as i/o can keep up