Re: [PATCH 8/8] qemu-options: Add the description of smp-cache object

[Zhao Liu <zhao1.liu@intel.com>]

Hi Markus,

On Mon, Jul 22, 2024 at 03:37:43PM +0200, Markus Armbruster wrote:
> Date: Mon, 22 Jul 2024 15:37:43 +0200
> From: Markus Armbruster <armbru@redhat.com>
> Subject: Re: [PATCH 8/8] qemu-options: Add the description of smp-cache
>  object
> 
> Zhao Liu <zhao1.liu@intel.com> writes:
> 
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> 
> This patch is just documentation.  The code got added in some previous
> patch.  Would it make sense to squash this patch into that previous
> patch?

OK, I'll merge them.

> > ---
> > Changes since RFC v2:
> >  * Rewrote the document of smp-cache object.
> >
> > Changes since RFC v1:
> >  * Use "*_cache=topo_level" as -smp example as the original "level"
> >    term for a cache has a totally different meaning. (Jonathan)
> > ---
> >  qemu-options.hx | 58 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 58 insertions(+)
> >
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 8ca7f34ef0c8..4b84f4508a6e 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -159,6 +159,15 @@ SRST
> >          ::
> >  
> >              -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512
> > +
> > +    ``smp-cache='id'``
> > +        Allows to configure cache property (now only the cache topology level).
> > +
> > +        For example:
> > +        ::
> > +
> > +            -object '{"qom-type":"smp-cache","id":"cache","caches":[{"name":"l1d","topo":"core"},{"name":"l1i","topo":"core"},{"name":"l2","topo":"module"},{"name":"l3","topo":"die"}]}'
> > +            -machine smp-cache=cache
> >  ERST
> >  
> >  DEF("M", HAS_ARG, QEMU_OPTION_M,
> > @@ -5871,6 +5880,55 @@ SRST
> >          ::
> >  
> >              (qemu) qom-set /objects/iothread1 poll-max-ns 100000
> > +
> > +    ``-object '{"qom-type":"smp-cache","id":id,"caches":[{"name":cache_name,"topo":cache_topo}]}'``
> > +        Create an smp-cache object that configures machine's cache
> > +        property. Currently, cache property only include cache topology
> > +        level.
> > +
> > +        This option must be written in JSON format to support JSON list.
> 
> Why?

I'm not familiar with this, so I hope you could educate me if I'm wrong.

All I know so far is for -object that defining a list can only be done in
JSON format and not with a numeric index like a keyval based option, like:

-object smp-cache,id=cache0,caches.0.name=l1i,caches.0.topo=core: Parameter 'caches' is missing

the above doesn't work.

Is there any other way to specify a list in command line?

> > +
> > +        The ``caches`` parameter accepts a list of cache property in JSON
> > +        format.
> > +
> > +        A list element requires the cache name to be specified in the
> > +        ``name`` parameter (currently ``l1d``, ``l1i``, ``l2`` and ``l3``
> > +        are supported). ``topo`` parameter accepts CPU topology levels
> > +        including ``thread``, ``core``, ``module``, ``cluster``, ``die``,
> > +        ``socket``, ``book``, ``drawer`` and ``default``. The ``topo``
> > +        parameter indicates CPUs winthin the same CPU topology container
> > +        are sharing the same cache.
> > +
> > +        Some machines may have their own cache topology model, and this
> > +        object may override the machine-specific cache topology setting
> > +        by specifying smp-cache object in the -machine. When specifying
> > +        the cache topology level of ``default``, it will honor the default
> > +        machine-specific cache topology setting. For other topology levels,
> > +        they will override the default setting.
> > +
> > +        An example list of caches to configure the cache model (l1d cache
> > +        per core, l1i cache per core, l2 cache per module and l3 cache per
> > +        socket) supported by PC machine might look like:
> > +
> > +        ::
> > +
> > +              {
> > +                "caches": [
> > +                   { "name": "l1d", "topo": "core" },
> > +                   { "name": "l1i", "topo": "core" },
> > +                   { "name": "l2", "topo": "module" },
> > +                   { "name": "l3", "topo": "socket" },
> > +                ]
> > +              }
> > +
> > +        An example smp-cache object would look like:()
> > +
> > +        .. parsed-literal::
> > +
> > +             # |qemu_system| \\
> > +                 ... \\
> > +                 -object '{"qom-type":"smp-cache","id":id,"caches":[{"name":cache_name,"topo":cache_topo}]}' \\
> > +                 ...
> >  ERST
>