<html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body> Hi everyone, In a scenario where running benchmarks on dedicated hardware is not possible, I'm trying to momentarily cap the I/O bandwidth used by interactive user sessions while benchmarks are running, in order to improve the stability of said benchmark's I/O performance. In the following discussion, I'll focus on capping the read bandwidth of /dev/sda for the sake of keeping my examples short, but if I can get this to work, the idea would be to cap the read and write bandwidth of all storage devices. From <a class="moz-txt-link-freetext" href="https://www.freedesktop.org/software/systemd/man/systemd.resource-control.html">https://www.freedesktop.org/software/systemd/man/systemd.resource-control.html</a> , I understand that I should be able to achieve the intended goal by... <ul> <li>Running something like `systemctl set-property --runtime user.slice IOReadBandwidthMax='/dev/sda 1M'` before the benchmark</li> <li>Running something like `systemctl set-property --runtime user.slice IOReadBandwidthMax=` after the benchmark.</li> </ul> However, this is not effective, as can be checked by running `hdparm -t`, which still observes the full disk bandwidth. I have tried the following variants: <ul> <li>`systemd-run -p IOReadBandwidthMax='/dev/sda 1M' -t bash` works (hdparm only sees 1 MB/s within the resulting shell) </li> <li>`systemd-run -t bash` followed by `systemctl set-property --runtime <new unit> IOReadBandwidthMax='/dev/sda 1M'` also works (hdparm only sees 1 MB/s).</li> <li>More specifically targeting individual users' slices (user-<uid>.slice) doesn't work. </li> </ul> This looks like a cgroups or systemd bug to me, but I thought I would cross-check with you before reporting this to my distribution's bugtracker (my distro packages systemd 246, which is just below your minimal version criterion for upstream bug reports). Should I be able to set I/O bandwidth caps on a top-level slice like user.slice, or is it expected that I can only do it on individual services? Cheers, Hadrien </body> </html>