[libvirt-users] What global_quota option mean? What's its logic?

[Ján Tomko]

On Thu, Nov 02, 2017 at 03:03:56PM +0200, Volo M. wrote:
>Hi techs,
>
>Could you please explain or refer me to documentation where I could find a
>description of global_quota schedinfo option. Someone told me that it could
>mean a cpu limitation in percents like:
>global_quota   : 25000 (does it mean cpu limit % set to 25  ?)
>

The _quota values are relative to the _period, both in milliseconds and refer
to the cumulative CPU time available to all the processes/threads in a group.

See the documentation in the kernel:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/scheduler/sched-bwc.txt

So with global_period being set to 100000, a value of 25000 would mean
that all the threads of the virtual machine would be limited to use at
most 25 % of 1 CPU.

>Is it true?
>What other parameters mean in below output?
>I didn't find any related documentation at libvirt.org.
>Could you help me to describe me or refer to some description what below
>schedinfo options mean? Thanks.
>

[...]

>
>[root at cpkvm ~]# virsh schedinfo 3 --set global_quota=25
>
>Scheduler      : posix
>
>error: invalid argument: value of 'global_quota' is out of range [1000,
>18446744073709551]
>
>[1000, 18446744073709551]  - what this range mean?
>

These are the minimum and maximum values that were accepted by the
kernel at the time when this error message was implemented in libvirt.

Jan
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