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Re: [PATCH v1 2/9] s390x: toplogy: adding drawers and books to smp parsi


From: Pierre Morel
Subject: Re: [PATCH v1 2/9] s390x: toplogy: adding drawers and books to smp parsing
Date: Tue, 20 Jul 2021 14:29:35 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0



On 7/20/21 11:19 AM, Daniel P. Berrangé wrote:
On Tue, Jul 20, 2021 at 10:46:31AM +0200, Pierre Morel wrote:


On 7/20/21 10:20 AM, Cornelia Huck wrote:
On Tue, Jul 20 2021, Pierre Morel <pmorel@linux.ibm.com> wrote:

On 7/19/21 5:50 PM, Cornelia Huck wrote:
On Fri, Jul 16 2021, Daniel P. Berrangé <berrange@redhat.com> wrote:
Is the book/drawer thing architecture specific, or is it machine
type / CPU specific. ie do /all/ the s390x machine types / CPUS
QEMU support the book/drawer concept, or only a subset.

Should not be by machine type, but might be by cpu model (e.g. older
hardware lacking the needed support for exposing this to the guest.) IBM
folks, please correct me if I'm wrong.


Looks correct to me this is an information indicated by a facility
introduced with Z10 if I do not make an error.

Hm. Would that become a problem if we made availability of parameters
dependent upon a value in the machine (see the other thread I cc:ed you
on?)


Why?
The parameter can always be there, it is just that with older cpu model we
will not report the topology information to the guest.

I mostly see this as an error reporting problem, perhaps with an optional
capabilitty reporting facility.

eg if someone requests 'z9'  or older together with books > 1 or
drawers > 1, it would be ideal if QEMU reports an error message,
rather than silently ignoring it and not reporting this info to
the guest.

Taking it further, it some app queries CPU models  via QMP, it
could be desirable if the CPU model data returned indicates whether
drawers/books > 1 are conceptually available.  Likewise for dies
on x86, since I cna't imagine guest OS doing sensible things
with an i486 CPU and dies=2

Regards,
Daniel


Thanks,
I will rework this based on what is done on x86 and dies.

regards,
Pierre

--
Pierre Morel
IBM Lab Boeblingen



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