Re: cgroups and nice

[Resending because gmail doesn't understand when to go plaintext :-) ]
[Added a few other folks who might have something to say about it]

On Fri, Nov 25, 2016 at 9:34 AM, Marat Khalili [off-list ref] wrote:

I have a question as a cgroup cpu limits user: how does it interact with
nice? Documentation creates the impression that, as long as number of
processes demanding the cpu time exceeds number of available cores, time
allocated will be proportional to configured cpu.shares. However, in
practice I observe that group with niced processes significantly under
perform.

For example, suppose on a 6-core box /cgroup/cpu/group1/cpu.shares is 400,
and /cgroup/cpu/group2/cpu.shares is 200.
1) If I run `stress -c 6` in both groups, I should see approximately 400% of
cpu time in group1 and 200% in group2 in top output, regardless of their
relative nice value.
2) If I run `nice -n 19 stress -c 1` in cgroup1 and `stress -c 24` in
group2, I should see at least 100% of cpu time in group1.

What I see is significantly less cpu time in group1 if group1 processes
happen to have greater nice value, and especially if group2 have greater
number of processes involved: cpu load of group1 in example 2 can be as low
as 20%. It may create tensions among users in my case; how can this be
avoided except by renicing all processes to the same value?

quoted

$ uname -a
Linux redacted 2.6.32-642.11.1.el6.x86_64 #1 SMP Fri Nov 18 19:25:05 UTC
2016 x86_64 x86_64 x86_64 GNU/Linux

This is an old version of the kernel. Do you see the same behavior on
a newer version of the kernel? (4.8 is the latest stable kernel)

quoted

$ lsb_release -a
LSB Version:
:base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
Distributor ID: CentOS
Description:    CentOS release 6.8 (Final)
Release:        6.8
Codename:       Final

(My apologies if I'm posting to incorrect list.)

--

With Best Regards,
Marat Khalili
--

Thanks,
Dhaval