[systemd-devel] systemd-cgtop doesn't show Input/Output

[Vladimir Mokrozub]

Thank you, I added "systemd.unified_cgroup_hierarchy=1 " to the kernel's
command line and systemd-cgtop now shows Input/Output.
However, I ran into a problem with LXC containers after switching to
unified mode and though I managed to solve it, I'm worried that something
else might break in the future.
Is it safe to switch to v2 mode?



On Mon, Dec 5, 2022 at 4:16 PM Michal Koutný <mkoutny at suse.com> wrote:

> Hello.
>
> On Mon, Dec 05, 2022 at 09:38:18AM +0300, Vladimir Mokrozub <
> mogaba2009 at gmail.com> wrote:
> > $ systemctl --version
> > systemd 245 (245.4-4ubuntu3.19)
> > +PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP
> > +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN
> > +PCRE2 default-hierarchy=hybrid
>                            ^^^^^^
> Unless you override this on kernel cmdline, it means (blk)io controller
> is in v1 mode.
>
> > systemd-cgtop always has "-" in both Input/s and Output/s columns. There
> > are no spikes, even under a high disk load.
> > I was testing it with "dd if=/dev/sda of=/dev/null". Here's the output:
> >
> > Control Group    Tasks   %CPU   Memory  Input/s Output/s
> > /                          214     101.5       3.7G           -        -
> > user.slice               15       99.6       2.9G           -        -
> > system.slice          97         0.4     95.4M           -        -
>
> 1) It won't have proper hierarchical behavior (thus no values for .slice
>    units, cgtop defaults to depth of 3 thus you may not see the active
>    leaves),
> 2) it won't charge writeback IO properly (just FYI, it's not relevant
>    to your example).
>
> If you can, I'd suggest you to switch to the unified mode if you want
> hierarchical IO accounting.
>
> HTH,
> Michal
>
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