Test of [PATCH] blk-throttle: simplify logic by token bucket algorithm

[Hong Zhiguo <honkiko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi, Vivek,

I tested the PATCH again for some basic hierarchical setup as I did
before.

Preparation
============
1) mount subsys blkio with "__DEVEL__sane_behavior"
2) Create 3 levels of directories under the blkio mount point:
    mkdir 1
    mkdir 1/2
    mkdir 1/2/3
    mkdir 4
3) start 4 bash sessions, write their PIDs into:
    1/cgroup.procs
    1/2/cgroup.procs
    1/2/3/cgroup.procs
    4/cgroup.procs
4) prepare 4 10MB files on sdb(ext4 fs)

Note: in below hierarchy graph:
    "[50k]" means configured value for read_bps_device is 50kB/s
    "[-]"   means unlimit configured
    "(50k)" means bandwidth reported by dd is 50kB/s

Test A: 1 process throttled by ancestor group
=============================================
Hierarchy set-up:
    (echo "8:16 204800" > 1/blkio.throttle.read_bps_device)
    |-- 1 [200k]
    |    `-- 2 [-]
    |         `-- 3 [-]
    `-- 4 [-]

dd within group 3:
    (drop cache then: dd if=10M-file-3 of=/dev/null)
Result:
    205kB/s (I did same test without the token-bucket patch, The
result is also 205kB/s)

dd within group 2:
    (drop cache then: dd if=10M-file-2 of=/dev/null)
Result:
    205kB/s

Test B: 4 processes in 3 levels of hierarchy, group 1 unlimited
===============================================================
Hierarchy set-up:
    echo "8:16 204800" > 1/blkio.throttle.read_bps_device
    echo "8:16 102400" > 1/2/blkio.throttle.read_bps_device
    echo "8:16 51200"  > 1/2/3/blkio.throttle.read_bps_device
    echo "8:16 51200"  > 4/blkio.throttle.read_bps_device
    |-- 1 [-]
    |    `-- 2 [100k]
    |         `-- 3 [50k]
    `-- 4 [50k]

start 4 dd processes from 4 bash sessions
    (dd if=10M-file-x of=/dev/null)
Result:
    |-- 1 (171M)
    |    `-- 2 (51.9k)
    |         `-- 3 (51.2k)
    `-- 4 (51.3k)

Test C: 4 processes in 3 levels of hierarchy
=============================================
Hierarchy set-up:
    echo "8:16 204800" > 1/blkio.throttle.read_bps_device
    echo "8:16 102400" > 1/2/blkio.throttle.read_bps_device
    echo "8:16 51200"  > 1/2/3/blkio.throttle.read_bps_device
    echo "8:16 51200"  > 4/blkio.throttle.read_bps_device
    |-- 1 [200k]
    |    `-- 2 [100k]
    |         `-- 3 [50k]
    `-- 4 [50k]

write 10M-file-1 to 20M, others still 10M, so 4 dd processes
take similar time.

start 4 dd processes from 4 bash sessions
    (dd if=10M-file-x of=/dev/null)
Result:
    |-- 1 (104k)
    |    `-- 2 (52.8k)
    |         `-- 3 (51.1k)
    `-- 4 (51.4k)