From: David Gibson <david@gibson.dropbear.id.au>
To: "Cédric Le Goater" <clg@kaod.org>
Cc: Laurent Vivier <lvivier@redhat.com>,
Thomas Huth <thuth@redhat.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Daniel Henrique Barboza <danielhb413@gmail.com>,
qemu-devel@nongnu.org, groug@kaod.org, qemu-ppc@nongnu.org,
Igor Mammedov <imammedo@redhat.com>
Subject: Re: [PATCH 1/2] spapr: number of SMP sockets must be equal to NUMA nodes
Date: Thu, 1 Apr 2021 13:53:48 +1100 [thread overview]
Message-ID: <YGU1vKCC9ER538dz@yekko.fritz.box> (raw)
In-Reply-To: <041ea566-62cd-0017-fbaa-bb56bd97d381@kaod.org>
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On Wed, Mar 31, 2021 at 05:22:39PM +0200, Cédric Le Goater wrote:
> On 3/31/21 6:58 AM, Michael Ellerman wrote:
> > David Gibson <david@gibson.dropbear.id.au> writes:
> >> On Mon, Mar 29, 2021 at 03:32:37PM -0300, Daniel Henrique Barboza wrote:
> > ...
> >>
> >>> We assign ibm,chip-id=0x0 to CPUs 0-3, but CPUs 2-3 are located in a
> >>> different NUMA node than 0-1. This would mean that the same socket
> >>> would belong to different NUMA nodes at the same time.
> >>
> >> Right... and I'm still not seeing why that's a problem. AFAICT that's
> >> a possible, if unexpected, situation under real hardware - though
> >> maybe not for POWER9 specifically.
> >
> > I think I agree.
> >
> >>> I believe this is what Cedric wants to be addressed. Given that the
> >>> property is called after the OPAL property ibm,chip-id, the kernel
> >>> expects that the property will have the same semantics as in OPAL.
> >>
> >> Even on powernv, I'm not clear why chip-id is tied into the NUMA
> >> configuration, rather than getting all the NUMA info from
> >> associativity properties.
> >
> > AFAIK we don't use chip-id for anything related to NUMA, if we do I'd
> > consider that a bug.
>
> Since PAPR only has NUMA nodes, is the use of chip-id in XIVE PAPR
> considered as a bug ? I would say so.
As noted in another thread, XIVE PAPR *doesn't* actually use chip_id.
And even on PowerNV, I don't think this has any real connection to
NUMA. For PowerNV we care about whether we're working within a single
XIVE hardware instance, or across multiple. There's one XIVE
per-chip, hence the relevance of chip-id. That happens to also match
to NUMA topology on (currently existing) POWER9 chips, but I don't see
that it inherently has to.
> > We do use it for topology_physical_package_id(), but that's almost
> > completely unused.
>
> In that case, I think it should be fine to return -1 like under PowerVM.
>
> Thanks,
>
> C.
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2021-04-01 3:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 18:34 [PATCH 0/2] pseries: SMP sockets must match NUMA nodes Daniel Henrique Barboza
2021-03-19 18:34 ` [PATCH 1/2] spapr: number of SMP sockets must be equal to " Daniel Henrique Barboza
2021-03-23 1:03 ` David Gibson
2021-03-23 17:21 ` Daniel Henrique Barboza
2021-03-25 2:10 ` David Gibson
2021-03-25 8:56 ` Cédric Le Goater
2021-03-25 10:15 ` Daniel Henrique Barboza
2021-03-29 4:20 ` David Gibson
2021-03-29 15:32 ` Cédric Le Goater
2021-03-29 18:32 ` Daniel Henrique Barboza
2021-03-29 23:55 ` Igor Mammedov
2021-03-31 0:57 ` David Gibson
2021-03-31 4:58 ` Michael Ellerman
2021-03-31 15:22 ` Cédric Le Goater
2021-04-01 2:53 ` David Gibson [this message]
2021-03-31 15:18 ` Cédric Le Goater
2021-03-31 17:29 ` Daniel Henrique Barboza
2021-03-31 17:40 ` Cédric Le Goater
2021-04-01 2:59 ` David Gibson
2021-04-01 9:21 ` Cédric Le Goater
2021-03-29 23:51 ` Igor Mammedov
2021-03-30 21:33 ` Daniel Henrique Barboza
2021-03-19 18:34 ` [PATCH 2/2] spapr.c: remove 'ibm,chip-id' from DT Daniel Henrique Barboza
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