From: Peter Maydell <peter.maydell@linaro.org>
To: David Hildenbrand <david@redhat.com>
Cc: "Thomas Huth" <thuth@redhat.com>,
"Daniel P . Berrangé" <berrange@redhat.com>,
"Janosch Frank" <frankja@linux.ibm.com>,
"Cornelia Huck" <cohuck@redhat.com>,
"Richard Henderson" <richard.henderson@linaro.org>,
"QEMU Developers" <qemu-devel@nongnu.org>,
"Markus Armbruster" <armbru@redhat.com>,
"Halil Pasic" <pasic@linux.ibm.com>,
"Christian Borntraeger" <borntraeger@de.ibm.com>,
qemu-s390x <qemu-s390x@nongnu.org>,
"Michael Mueller" <mimu@linux.ibm.com>,
"Jiri Denemark" <jdenemar@redhat.com>,
"Eduardo Habkost" <ehabkost@redhat.com>
Subject: Re: [PATCH v1 0/2] s390x/cpumodel: Introduce "best" model variants
Date: Fri, 8 Nov 2019 13:02:28 +0000 [thread overview]
Message-ID: <CAFEAcA-4r53vM-K24WYr1OFSOufhZ7hDHeZBhnywyaJ0gpMO1g@mail.gmail.com> (raw)
In-Reply-To: <5dd613c0-6d9e-b943-b64d-7ba1791cbefe@redhat.com>
On Fri, 8 Nov 2019 at 12:46, David Hildenbrand <david@redhat.com> wrote:
> There is a small but important difference between "max"/"host" and
> "best". Max really means "all features", including deprecated ones.
> "best", however, can disable experimental or deprecated features. Or any
> other features we don't want to be enabled when somebody selects a model
> manually.
>
> On s390x, the feature "csske" is deprecated. New HW still has it, but we
> want new guests to run without this facility. Dropping it from "max"
> would affect existing setups. We already changed the default model
> (e.g., -cpu z13) to disable it with never QEMU machines.
>
> E.g., nested virtualization features on some architectures could be a
> feature set you want to disable, although contained in the "max" model.
> (e.g., no migration support yet).
>
>
> I am not completely against calling these "max" models instead of "best"
> models, but I think this makes it clearer that there is indeed a difference.
Hmm. I see the distinction, but is it one that's sufficiently
worth making that we want to expose it to our users, possibly
try to add it to the other architectures, etc ? How bad is it
if the CPU provides some legacy deprecated feature that the
guest just doesn't use ?
'max' already shouldn't include experimental features, at least
for Arm -- those should be off by default, because they're
experimental and you only want users to get them if they
explicitly opt in via '-cpu something,+x-my-feature'.
thanks
-- PMM
next prev parent reply other threads:[~2019-11-08 13:03 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 11:07 [PATCH v1 0/2] s390x/cpumodel: Introduce "best" model variants David Hildenbrand
2019-11-08 11:07 ` [PATCH v1 1/2] s390x/cpumodels: Factor out CPU feature dependencies David Hildenbrand
2019-11-08 11:07 ` [PATCH v1 2/2] s390x/cpumodel: Introduce "best" model variants David Hildenbrand
2019-11-08 19:51 ` Eduardo Habkost
2019-11-08 21:18 ` David Hildenbrand
2019-11-08 11:10 ` [PATCH v1 0/2] " Peter Maydell
2019-11-08 12:46 ` David Hildenbrand
2019-11-08 13:02 ` Peter Maydell [this message]
2019-11-08 19:10 ` Eduardo Habkost
2019-11-08 22:58 ` David Hildenbrand
2019-11-09 16:07 ` Peter Maydell
2019-11-18 10:47 ` David Hildenbrand
2019-11-18 10:53 ` Peter Maydell
2019-11-18 10:56 ` David Hildenbrand
2019-11-18 10:59 ` Peter Maydell
2019-11-18 18:49 ` Eduardo Habkost
2019-11-18 21:19 ` Peter Maydell
2019-11-18 22:04 ` Eduardo Habkost
2019-11-19 9:22 ` Peter Maydell
2019-11-19 9:58 ` David Hildenbrand
2019-11-19 10:36 ` Peter Maydell
2019-11-19 11:00 ` David Hildenbrand
2019-11-19 19:42 ` Eduardo Habkost
2019-11-20 10:28 ` David Hildenbrand
2019-11-20 14:04 ` Eduardo Habkost
2019-11-20 14:21 ` David Hildenbrand
2019-11-08 16:59 ` no-reply
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