From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: thuth@redhat.com, ehabkost@redhat.com,
Pierre Morel <pmorel@linux.ibm.com>,
david@redhat.com, richard.henderson@linaro.org,
qemu-devel@nongnu.org, armbru@redhat.com, pasic@linux.ibm.com,
borntraeger@de.ibm.com, qemu-s390x@nongnu.org,
pbonzini@redhat.com, eblake@redhat.com
Subject: Re: [PATCH v1 1/9] s390x: smp: s390x dedicated smp parsing
Date: Mon, 19 Jul 2021 16:52:02 +0100 [thread overview]
Message-ID: <YPWfol5y2pdK9mtC@redhat.com> (raw)
In-Reply-To: <87fswa9un2.fsf@redhat.com>
On Mon, Jul 19, 2021 at 05:43:29PM +0200, Cornelia Huck wrote:
> (restored cc:s)
>
> On Fri, Jul 16 2021, Pierre Morel <pmorel@linux.ibm.com> wrote:
>
> > On 7/16/21 11:14 AM, Daniel P. Berrangé wrote:
> >> I increasingly worry that we're making a mistake by going down the
> >> route of having custom smp_parse implementations per target, as this
> >> is showing signs of inconsistent behaviour and error reportings. I
> >> think the differences / restrictions have granularity at a different
> >> level that is being tested in many cases too.
> >>
> >> Whether threads != 1 is valid will likely vary depending on what
> >> CPU model is chosen, rather than what architecture is chosen.
> >> The same is true for dies != 1. We're not really checking this
> >> closely even in x86 - for example I can request nonsense such
> >> as a 25 year old i486 CPU model with hyperthreading and multiple
> >> dies
> >>
> >> qemu-system-x86_64 -cpu 486 -smp 16,cores=4,dies=2,threads=2
>
> Now that's what I'd call an upgrade :)
>
> >>
> >> In this patch, there is no error reporting if the user specifies
> >> dies != 1 or threads != 1 - it just silently ignores the request
> >> which is not good.
> >
> > yes, I should change this
> >
> >>
> >> Some machine types may have constraints on CPU sockets.
> >>
> >> This can of course all be handled by custom smp_parse impls, but
> >> this is ultimately going to lead to alot of duplicated and
> >> inconsistent logic I fear.
> >>
> >> I wonder if we would be better off having machine class callback
> >> that can report topology constraints for the current configuration,
> >> along lines ofsmp_constraints(MachineState *ms,
> >>
> >> smp_constraints(MachineState *ms,
> >> int *max_sockets,
> >> int *max_dies,
> >> int *max_cores,
> >> int *max_threads)
> >
> > I find the idee good, but what about making it really machine agnostic
> > by removing names and using a generic
> >
> > smp_constraints(MachineState *ms,
> > int *nb_levels,
> > int *levels[]
> > );
> >
> > Level can be replaced by another name like container.
> > The machine could also provide the level/container names according to
> > its internal documentation.
>
> In theory, this could give us more flexibility; however, wouldn't
> that still mean that the core needs to have some knowledge of the
> individual levels? We also have the command line parsing to consider,
> and that one uses concrete names (which may or may not make sense,
> depending on what machine you are trying to configure), and we'd still
> have to map these to 'levels'.
Yeah, we need to deal with names in several places, so I don't think
abstracting it in one place is desirable, as it introduces the need
to convert between the two and potentially obscures the semantics.
Regards,
Daniel
--
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next prev parent reply other threads:[~2021-07-19 15:53 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 16:53 [PATCH v1 0/9] s390x: CPU Topology Pierre Morel
2021-07-14 16:53 ` [PATCH v1 1/9] s390x: smp: s390x dedicated smp parsing Pierre Morel
2021-07-16 8:54 ` Cornelia Huck
2021-07-16 9:14 ` Daniel P. Berrangé
2021-07-16 10:59 ` Pierre Morel
[not found] ` <e4865ad6-f8ec-e7ba-66ef-9c95334ba9b3@linux.ibm.com>
2021-07-19 15:43 ` Cornelia Huck
2021-07-19 15:52 ` Daniel P. Berrangé [this message]
2021-07-20 7:37 ` Pierre Morel
2021-07-20 8:33 ` Pierre Morel
2021-07-16 10:47 ` Pierre Morel
2021-07-14 16:53 ` [PATCH v1 2/9] s390x: toplogy: adding drawers and books to " Pierre Morel
2021-07-15 6:16 ` Markus Armbruster
2021-07-15 8:19 ` Pierre Morel
2021-07-15 10:48 ` Markus Armbruster
2021-07-16 9:10 ` Cornelia Huck
2021-07-16 9:18 ` Daniel P. Berrangé
2021-07-16 10:44 ` Cornelia Huck
2021-07-16 10:49 ` Daniel P. Berrangé
2021-07-19 15:50 ` Cornelia Huck
2021-07-20 7:52 ` Pierre Morel
2021-07-20 8:20 ` Cornelia Huck
2021-07-20 8:46 ` Pierre Morel
2021-07-20 9:00 ` Cornelia Huck
2021-07-20 9:19 ` Daniel P. Berrangé
2021-07-20 12:29 ` Pierre Morel
2021-07-16 9:23 ` Daniel P. Berrangé
2021-07-16 11:08 ` Pierre Morel
2021-07-14 16:53 ` [PATCH v1 3/9] s390x: cpu topology: CPU topology objects and structures Pierre Morel
2021-07-14 16:53 ` [PATCH v1 4/9] s390x: Topology list entries and SYSIB 15.x.x Pierre Morel
2021-07-14 16:53 ` [PATCH v1 5/9] s390x: topology: implementating Store Topology System Information Pierre Morel
2021-07-14 16:53 ` [PATCH v1 6/9] s390x: kvm: topology: interception of PTF instruction Pierre Morel
2021-07-16 9:22 ` Cornelia Huck
2021-07-16 11:23 ` Pierre Morel
2021-07-16 11:56 ` Cornelia Huck
2021-07-14 16:53 ` [PATCH v1 7/9] s390x: SCLP: reporting the maximum nested topology entries Pierre Morel
2021-07-16 9:24 ` Cornelia Huck
2021-07-16 11:12 ` Pierre Morel
2021-07-14 16:53 ` [PATCH v1 8/9] s390x: numa: define drawers and books for NUMA Pierre Morel
2021-07-14 16:53 ` [PATCH v1 9/9] s390x: numa: implement NUMA for S390x Pierre Morel
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