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

[Michal Koutný]

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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