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However, if I only set wbps, then everything works as expected. To reproduce the problem, we can follow these command-based steps: 1. **System Information:** - Kernel Version and OS Release: ``` $ uname -r 6.10.0-rc5+ $ cat /etc/os-release PRETTY_NAME="Ubuntu 24.04 LTS" NAME="Ubuntu" VERSION_ID="24.04" VERSION="24.04 LTS (Noble Numbat)" VERSION_CODENAME=noble ID=ubuntu ID_LIKE=debian HOME_URL="https://www.ubuntu.com/" SUPPORT_URL="https://help.ubuntu.com/" BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/" PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy" UBUNTU_CODENAME=noble LOGO=ubuntu-logo ``` 2. **Device Information and Settings:** - List Block Devices and Scheduler: ``` $ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS sda 8:0 0 4.4T 0 disk └─sda1 8:1 0 4.4T 0 part /data ... $ cat /sys/block/sda/queue/scheduler none [mq-deadline] kyber bfq $ cat /sys/block/sda/queue/rotational 1 ``` 3. **Reproducing the problem:** - Navigate to the cgroup v2 filesystem and configure I/O settings: ``` $ cd /sys/fs/cgroup/ $ stat -fc %T /sys/fs/cgroup cgroup2fs $ mkdir test $ echo "8:0 wbps=10485760 wiops=100000" > io.max ``` In this setup: wbps=10485760 sets the write bytes per second limit to 10 MB/s. wiops=100000 sets the write I/O operations per second limit to 100,000. - Add process to the cgroup and verify: ``` $ echo $$ > cgroup.procs $ cat cgroup.procs 3826771 3828513 $ ps -ef|grep 3826771 root 3826771 3826768 0 22:04 pts/1 00:00:00 -bash root 3828761 3826771 0 22:06 pts/1 00:00:00 ps -ef root 3828762 3826771 0 22:06 pts/1 00:00:00 grep --color=auto 3826771 ``` - Observe I/O performance using `dd` commands and `iostat`: ``` $ dd if=/dev/zero of=/data/file1 bs=512M count=1 & $ dd if=/dev/zero of=/data/file1 bs=512M count=1 & ``` ``` $ iostat -d 1 -h -y -p sda tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 7.00 0.0k 1.3M 0.0k 0.0k 1.3M 0.0k sda 7.00 0.0k 1.3M 0.0k 0.0k 1.3M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 21.00 0.0k 1.4M 0.0k 0.0k 1.4M 0.0k sda 21.00 0.0k 1.4M 0.0k 0.0k 1.4M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda 5.00 0.0k 1.2M 0.0k 0.0k 1.2M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 1848.00 0.0k 448.1M 0.0k 0.0k 448.1M 0.0k sda 1848.00 0.0k 448.1M 0.0k 0.0k 448.1M 0.0k sda1 ``` Initially, the write speed is slow (<2MB/s) then suddenly bursts to several hundreds of MB/s. - Testing with wiops set to max: ``` echo "8:0 wbps=10485760 wiops=max" > io.max $ dd if=/dev/zero of=/data/file1 bs=512M count=1 & $ dd if=/dev/zero of=/data/file1 bs=512M count=1 & ``` ``` $ iostat -d 1 -h -y -p sda tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 48.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda 48.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 40.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda 40.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 41.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda 41.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 46.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda 46.00 0.0k 10.0M 0.0k 0.0k 10.0M 0.0k sda1 tps kB_read/s kB_wrtn/s kB_dscd/s kB_read kB_wrtn kB_dscd Device 55.00 0.0k 10.2M 0.0k 0.0k 10.2M 0.0k sda 55.00 0.0k 10.2M 0.0k 0.0k 10.2M 0.0k sda1 ``` The iostat output shows the write operations as stabilizing at around 10 MB/s, which aligns with the defined limit of 10 MB/s. After setting wiops to max, the I/O limits appear to work as expected. Thanks, Lance