Cc linux-kernel mail list
on 2016/5/11 at 22:15, Miao Xie wrote:
Hi, Tejun and Fengguang
I found that buffered write thoughput was dropped down by writeback cgroup and
dirty thottle on
4.6-rc7 kernel. If I ran benchmark on the top block cgroup, the thoughput was
more than 1500MB/s.
If I ran benchmark on a new block cgroup, the thoughput was down to 4MB/s.
Steps to reproduce:
# mount -t cgroup2 cgroup <cgrp_mnt>
# echo "+io +memory" > <cgrp_mnt>/cgroup.subtree_control
# mkdir <cgrp_mnt>/aaa
# echo $$ > <cgrp_mnt>/aaa/cgroup.procs
# fio test.config
job0: (g=0): rw=write, bs=4K-4K/4K-4K/4K-4K, ioengine=psync, iodepth=1
fio-2.2.8
Starting 1 thread
Jobs: 1 (f=1): [W(1)] [3.7% done] [0KB/4000KB/0KB /s] [0/1000/0 iops] [eta
04m:50s]
Fio configuration is:
[global]
bs=4K
direct=0
ioengine=psync
iodepth=1
directory=/mnt/ext4/tstdir0
time_based
runtime=300
group_reporting
size=16G
sync=0
max_latency=120000000
thread
[job0]
numjobs=1
rw=write
My box has 48 cores and 188GB memory, but I set
vm.dirty_background_bytes = 268435456
vm.dirty_bytes = 536870912
if I set vm.dirty_background_bytes and vm.dirty_bytes to be a large
number(vm.dirty_background_bytes = 3GB,
vm.dirty_bytes = 4GB), then fio thoughput would be more than 1500MB/s. and then
if I reset them to the original
value(the above ones), the thoughout would be down to 500MB/s.
And according my debug, I found fio sleeped for 1ms every time we dirty a
page(balance dirty pages) when
the thoughput was down to 4MB/s, it might be a bug of dirty throttle when we
open write back cgroup, I think.
Tejun and Fengguang, please let me know what you guys think about this issue,
and if you have
any suggestions for possible solutions, Any input is greatly appreciated!
Thanks
Miao
