Re: [PATCH v23 01/20] CPU topology: extend with s390 specifics

[Markus Armbruster]

Nina Schoetterl-Glausch <nsg@linux.ibm.com> writes:

> On Wed, 2023-09-20 at 13:11 +0200, Markus Armbruster wrote:
>> Nina Schoetterl-Glausch <nsg@linux.ibm.com> writes:
>> 
>> > From: Pierre Morel <pmorel@linux.ibm.com>
>> > 
>> > S390 adds two new SMP levels, drawers and books to the CPU
>> > topology.
>> > S390 CPUs have specific topology features like dedication and
>> > entitlement. These indicate to the guest information on host
>> > vCPU scheduling and help the guest make better scheduling decisions.
>> > 
>> > Let us provide the SMP properties with books and drawers levels
>> > and S390 CPU with dedication and entitlement,
>> > 
>> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> > Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> > Co-developed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> > Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
>> > diff --git a/qapi/machine-common.json b/qapi/machine-common.json
>> > new file mode 100644
>> > index 0000000000..e40421bb37
>> > --- /dev/null
>> > +++ b/qapi/machine-common.json
>> > @@ -0,0 +1,21 @@
>> > +# -*- Mode: Python -*-
>> > +# vim: filetype=python
>> > +#
>> > +# This work is licensed under the terms of the GNU GPL, version 2 or 
>> > later.
>> > +# See the COPYING file in the top-level directory.
>> > +
>> > +##
>> > +# = Machines S390 data types
>> > +##
>> > +
>> > +##
>> > +# @CpuS390Entitlement:
>> > +#
>> > +# An enumeration of cpu entitlements that can be assumed by a virtual
>> > +# S390 CPU
>> 
>> CPU entitlements
>> 
>> Would someone reasonably familiar with S390 understand this?  Because
>
> Well, someone familiar with s390 topology would, otherwise probably not tbh.

Good enough, I guess.

>> I'm not and I don't; I wonder what "a virtual CPU assuming an
>> entitlement" means.
>
> Basically, on s390x the OS is always running on some hypervisor.
> Even without KVM or z/VM you can slice up the machine, namely into logical
> partitions (LPARs). Therefore, there is a scheduling of virtual CPUs to the
> actual physical ones. "Entitlement" is a statement about how that scheduling
> works for a virtual CPU. The same concepts can then also be applied to KVM.

Thanks!

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