Can't throttle IO on cgroup. Says "No such device" when device exists. What could be wrong?

Question

Instructions I followed: https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v1/blkio-controller.html

Script I ran:

 
 BYTES_PER_SEC=1048576;
 
 MAJOR=259
 MINOR=1
 
 echo "device name:"
 udevadm info -rq name /sys/dev/block/$MAJOR:$MINOR
 echo ""
 echo "device numbers:"
 echo $MAJOR:$MINOR;
 echo ""
 
 sudo mount -t cgroup -o blkio none /sys/fs/cgroup/blkio;
 sudo echo "COMMAND TO BE EXECUTED:";
 sudo echo "$MAJOR:$MINOR  $BYTES_PER_SEC";
 sudo echo "$MAJOR:$MINOR  $BYTES_PER_SEC" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
 sudo echo "$MAJOR:$MINOR  $BYTES_PER_SEC" > /sys/fs/cgroup/blkio/blkio.throttle.write_bps_device

Output:

~/Desktop >>> sudo ./test.sh                                                                                                                                                                                   [1]
[sudo] password for brian: 
/dev/nvme0n1p1
device name: 259:1
mount: /sys/fs/cgroup/blkio: none already mounted on /sys/fs/bpf.
COMMAND TO BE EXECUTED:
259:1  1048576
echo: write error: No such device
echo: write error: No such device

Not sure what could be wrong. I'm also using NixOS here so not sure if that will actually effect the results.

score -1 · Accepted Answer · answered Jun 01 '21 at 17:25

The error occurs because the only way to throttle IO using cgroups version 1 is to use a device that is physical. The major and minor version numbers I used above are for a partition. You need to pick the major and minor numbers for the physical device that HOLDS the partition.

Can't throttle IO on cgroup. Says "No such device" when device exists. What could be wrong?

1 Answers1