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

[Barry Scott]

> On 6 Dec 2022, at 06:45, Vladimir Mokrozub <mogaba2009 at gmail.com> wrote:
> 
> 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?

Better question is this; Is it safe to stay on the legacy V1 with its missing features and no new development?

At some point you will have to fix the issues if you depend on legacy v1 cgroups.
The v1 support is being dropped from systemd at some point I think.

Barry

> 
> 
> 
> On Mon, Dec 5, 2022 at 4:16 PM Michal Koutný <mkoutny at suse.com <mailto:mkoutny at suse.com>> wrote:
>> Hello.
>> 
>> On Mon, Dec 05, 2022 at 09:38:18AM +0300, Vladimir Mokrozub <mogaba2009 at gmail.com <mailto: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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