[Users] IOPRIO and blkio.weight not working
Simon Boulet
simon at nostalgeek.com
Thu Dec 27 14:50:17 EST 2012
Hi,
Setting IOPRIO doesn't seem to properly distribute I/O for my VEs. I
checked the Cgroup blkio and confirmed the blkio.weight is set in scale
with the IOPRIO of each VE conf.
I tested ex. setting blkio.throttle.write_bps_device and confirmed Cgroup
blkio is properly working (setting it to 1024000 does limit the VE to about
1MB/sec). I also checked the processes are properly listed in the Cgroup
tasks. However, blkio.weight really doesn't seems to be doing anyting.
I'm using the latest stable 2.6.32-042stab068.8.
To test the I/O performance from inside my VE, I run the following in two
separate VE, one with an IOPRIO of 1 (blkio.weight of 365) and the other
with an IOPRIO of 7 (blkio.weight of 640) :
while [ 1 ]; do dd if=/dev/zero of=test bs=1M count=100 oflag=direct; done
Both give about the same results.
The same seems to apply with plain ionice. I get very similar I/O
performances independently of the Best-Effort priority I set. However
setting one process in the Idle class and the other in Best-Effort does
make a difference.
I double checked and I am using the CFQ scheduler. Also my VE private
directory are on top of an LVM volume, not sure if that could have an
impact.
Thanks
Simon
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