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

[Markus Armbruster <armbru@redhat.com>]

Zhao Liu <zhao1.liu@intel.com> writes:

> On Thu, Jul 25, 2024 at 11:07:12AM +0200, Markus Armbruster wrote:
>> Date: Thu, 25 Jul 2024 11:07:12 +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:
>> 
>> > Hi Markus and Daniel,
>> >
>> > I have the questions about the -object per cache implementation:
>> >
>> > On Wed, Jul 24, 2024 at 02:39:29PM +0200, Markus Armbruster wrote:
>> >> Date: Wed, 24 Jul 2024 14:39:29 +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:
>> >> 
>> >> > 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 command line is a big, sprawling mess :)
>> >> 
>> >> -object supports either a JSON or a QemuOpts argument.  *Not* keyval!
>> >> 
>> >> Both QemuOpts and keyval parse something like KEY=VALUE,...  Keyval
>> >> supports arrays and objects via dotted keys.  QemuOpts doesn't natively
>> >> support arrays and objects, but its users can hack around that
>> >> limitation in various ways.  -object doesn't.  So you're right, it's
>> >> JSON or bust here.
>> >> 
>> >> However, if we used one object per cache instead, we could get something
>> >> like
>> >> 
>> >>     -object smp-cache,name=l1d,...
>> >>     -object smp-cache,name=l1u,...
>> >>     -object smp-cache,name=l2,...
>> >>     ...
>> >
>> > Current, I use -object to create a smp_cache object, and link it to
>> > MachineState by -machine,smp-cache=obj_id.
>> >
>> > Then for the objects per cache, how could I link them to machine?
>> >
>> > Is it possible that I create something static in smp_cache.c and expose
>> > all the cache information to machine through some interface?
>> 
>> Good questions.  However, before we head deeper into the weeds here, I
>> feel we should discuss the things below.  And before we do that, I need
>> a clear understanding of the use case.  Elsewhere in this thread, I just
>> described the use case as I understand it.  Please reply there.  I'll
>> then come back to this message.
>> 
>> [...]
>
> Jonathan and I provided different use cases for x86 and Arm. Could we
> come back here to continue the discussion? :)

Can you provide a brief summary of the design alternatives that have
been proposed so far?  Because I've lost track.