Re: [PATCH v2] blk-throttle: simplify logic by token bucket algorithm

[Hong zhi guo]

Hi, Tejun,

I did the test for 3 levels hierarchy. It works.

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
3) start 3 bash sessions, write their PIDs into:
    1/cgroup.procs
    1/2/cgroup.procs
    1/2/3/cgroup.procs
4) prepare 3 10MB files on sdb(ext4 fs)

Note: in below hierarchy graph:
    "[50k]" means configured value for read_bps_device is 50kB/s
    "(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 [-]

dd within group 3:
    (drop cache then: dd if=10M-file-3 of=/dev/null)
Result:
    206kB/s (I did same test without the token-bucket patch, The
result is 205kB/s)

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


Test B: 3 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
    1 [200k]
    `-- 2 [100k]
        `-- 3 [50k]
start 3 dd processes from 3 bash sessions
    (dd if=10M-file-x of=/dev/null)
Result:
    1 (103k)
    `-- 2 (51.9k)
        `-- 3 (51.4k)


best regards
Hong Zhiguo
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