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

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Tue, 2023-09-19 at 14:47 +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>
> > ---
> >  qapi/machine-common.json            | 21 +++++++++++++
> >  qapi/machine.json                   | 19 ++++++++++--
> >  include/hw/boards.h                 | 10 +++++-
> >  include/hw/qdev-properties-system.h |  4 +++
> >  target/s390x/cpu.h                  |  6 ++++
> >  hw/core/machine-smp.c               | 48 ++++++++++++++++++++++++-----
> >  hw/core/machine.c                   |  4 +++
> >  hw/core/qdev-properties-system.c    | 13 ++++++++
> >  hw/s390x/s390-virtio-ccw.c          |  4 +++
> >  softmmu/vl.c                        |  6 ++++
> >  target/s390x/cpu.c                  |  7 +++++
> >  qapi/meson.build                    |  1 +
> >  qemu-options.hx                     |  7 +++--
> >  13 files changed, 137 insertions(+), 13 deletions(-)
> >  create mode 100644 qapi/machine-common.json
> > 
> > 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
> 
> Why do you need a separate QAPI sub-module?

See here https://lore.kernel.org/qemu-devel/d8da6f7d1e3addcb63614f548ed77ac1b8895e63.camel@linux.ibm.com/
> 
> > @@ -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
> > +#
> > +# Since: 8.2
> > +##
> > +{ 'enum': 'CpuS390Entitlement',
> > +  'prefix': 'S390_CPU_ENTITLEMENT',
> > +  'data': [ 'auto', 'low', 'medium', 'high' ] }
> > diff --git a/qapi/machine.json b/qapi/machine.json
> > index a08b6576ca..a63cb951d2 100644
> > --- a/qapi/machine.json
> > +++ b/qapi/machine.json
> > @@ -9,6 +9,7 @@
>    ##
>    # = Machines
> >  ##
> >  
> >  { 'include': 'common.json' }
> > +{ 'include': 'machine-common.json' }
> 
> Section structure is borked :)
> 
> Existing section "Machine" now ends at the new "Machines S390 data
> types" you pull in here.  The contents of below moves from "Machines" to
> "Machines S390 data types".
> 
> Before I explain how to avoid this, I'd like to understand why we need a
> new sub-module.
> 
> >  
> >  ##
> >  # @SysEmuTarget:
> > @@ -71,7 +72,7 @@
>    ##
>    # @CpuInfoFast:
>    #
>    # Information about a virtual CPU
>    #
>    # @cpu-index: index of the virtual CPU
>    #
>    # @qom-path: path to the CPU object in the QOM tree
> >  #
> >  # @thread-id: ID of the underlying host thread
> >  #
> > -# @props: properties describing to which node/socket/core/thread
> > +# @props: properties describing to which node/drawer/book/socket/core/thread
> >  #     virtual CPU belongs to, provided if supported by board
> 
> Is this description accurate?

Kinda, although the wording might not be the best.
All the CpuInstanceProperties fields are optional, it's like a superset of possible
properties across architectures.
Only a subset might be returned by query-cpus-fast.
Also die and cluster are missing.
> 
> @props is of type CpuInstanceProperties, shown below.  Its documentation
> describes it as "properties to be used for hotplugging a CPU instance,
> it should be passed by management with device_add command when a CPU is
> being hotplugged."  Hmm.
> 
> I figure details ("node/drawer/book/socket/core/thread") are better left
> to CpuInstanceProperties.
> 
> The "provided if supported by board" part makes no sense to me.  If
> @props is there, it lists the properties we need to provide with
> device_add.  What if it's not there?  Same as empty list, i.e. we don't
> need to provide properties with device_add?

There are default values/default logic.
For s390x, socket, book, drawer are calculated from the core id
if not provided with device_add.
Partial specifications are rejected.

> 
> Not your patch's fault, but let's get this in shape if we can.
> 
> >  #
> >  # @target: the QEMU system emulation target, which determines which
> > @@ -901,7 +902,11 @@
> >  #
> >  # @node-id: NUMA node ID the CPU belongs to
> >  #
> > -# @socket-id: socket number within node/board the CPU belongs to
> > +# @drawer-id: drawer number within node/board the CPU belongs to (since 8.2)
> > +#
> > +# @book-id: book number within drawer/node/board the CPU belongs to (since 8.2)
> 
> Long lines, please wrap:
> 
>    # @drawer-id: drawer number within node/board the CPU belongs to
>    #     (since 8.2)
>    #
>    # @book-id: book number within drawer/node/board the CPU belongs to
>    #     (since 8.2)

Ok.
> 
> > +#
> > +# @socket-id: socket number within book/node/board the CPU belongs to
> >  #
> >  # @die-id: die number within socket the CPU belongs to (since 4.1)
> >  #
> > @@ -912,7 +917,7 @@
>    ##
>    # @CpuInstanceProperties:
>    #
>    # List of properties to be used for hotplugging a CPU instance, it
>    # should be passed by management with device_add command when a CPU is
>    # being hotplugged.
>    #
>    # @node-id: NUMA node ID the CPU belongs to
>    #
>    # @socket-id: socket number within node/board the CPU belongs to
>    #
>    # @die-id: die number within socket the CPU belongs to (since 4.1)
>    #
>    # @cluster-id: cluster number within die the CPU belongs to (since
>    #     7.1)
>    #
>    # @core-id: core number within cluster the CPU belongs to
> >  #
> >  # @thread-id: thread number within core the CPU belongs to
> >  #
> > -# Note: currently there are 6 properties that could be present but
> > +# Note: currently there are 8 properties that could be present but
> >  #     management should be prepared to pass through other properties
> >  #     with device_add command to allow for future interface extension.
> >  #     This also requires the filed names to be kept in sync with the
>    #     properties passed to -device/device_add.
> 
> The last sentence is for developers, not for users, which means it
> doesn't belong here.  Suggest to move it to a non-doc comment, and
> rephrase the note like
> 
>    # Note: management should be prepared to pass through additional
>    # properties with device_add.
> 
> > @@ -922,6 +927,8 @@
> >  ##
> >  { 'struct': 'CpuInstanceProperties',
> 
> Non-doc comment could go here:
> 
>      # Keep these in sync with the properties device_add accepts
> 
> Again, not your patch's fault, but your help improving this stuff would
> be appreciated.
> 
> >    'data': { '*node-id': 'int',
> > +            '*drawer-id': 'int',
> > +            '*book-id': 'int',
> >              '*socket-id': 'int',
> >              '*die-id': 'int',
> >              '*cluster-id': 'int',
>                '*core-id': 'int',
>                '*thread-id': 'int'
>      }
>    }
> 

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