linux-kernel - Re: [PATCH v6 00/21] arch_topology: Updates to add socket support and fix cluster ids

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Date:   Tue, 5 Jul 2022 21:07:37 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Conor.Dooley@...rochip.com
Cc:     Brice.Goglin@...ia.fr, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org,
        Valentina.FernandezAlanis@...rochip.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        wangqing@...o.com, robh+dt@...nel.org, rafael@...nel.org,
        ionela.voinescu@....com, pierre.gondois@....com,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kernel@...il.dk
Subject: Re: [PATCH v6 00/21] arch_topology: Updates to add socket support
 and fix cluster ids

On Tue, Jul 05, 2022 at 07:06:17PM +0000, Conor.Dooley@...rochip.com wrote:
> [Adding back the CC list from the original thread]
> 
> On 05/07/2022 13:27, Brice Goglin wrote:
> > [You don't often get email from brice.goglin@...ia.fr. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> > 
> > Hello Conor
> > 
> > I am the main developer of hwloc [1] which is used by many people to
> > detect the topology of servers. We're started to see some users of hwloc
> > on RISC-V and we got some reports about the topology exposed by
> > Linux/sysfs being wrong on some platforms.
> > 
> > For instance https://github.com/open-mpi/hwloc/issues/536 says HiFive
> > Unmatched with SiFive Freedom U740 running Linux 5.15 exposes a single
> > core with 4 threads instead of 4 cores, while StarFive VisionFive v1
> > with JH7100 running 5.18.5 correctly exposes 2 cores.
> 
> And with Sudeep's patches applied I get (next-20220704):
> # hwloc-calc -N core all
> 1
> # hwloc-calc -N pu all
> 4
> On a PolarFire SoC (so the same as a SiFive U540).
> So unfortunately, these patches are not the fix you seek!
>

Not sure what you mean by that ?

> Wracked my brains for a bit, but could not see any differences
> between the U740 and the JH7100. Culprit seems to be the lack
> of a cpu-map node (which is only present in the downstream dt).
>

Indeed, the topology depends on /cpu-map node. However on ARM64 we do
have fallback settings in absence of /cpu-map node so that it is handled
correctly. I wasn't sure what was or can be done on RISC-V as /cpu-map
is optional.

> I've sent patches for the upstream devicetrees:
> https://lore.kernel.org/linux-riscv/20220705190435.1790466-1-mail@conchuod.ie/
>

I will take a look.

> > Does it depend a lot on the platform because
> > device-tree and/or ACPI aren't always properly filled by vendors?

Absolutely.

> > Does it depend a lot on the Linux kernel version?

Ideally not much, but hey we had some issues on Arm64 too which this series
is addressing.

> > Should I expect significant improvements for both in the next months?

Not much in topology or nothing planned. I have no idea on NUMA


Hi Conor,

I would have preferred you to add me to the original thread and referred
this thread from there. I don't want to derail the discussion in this
thread as nothing much can be done here.

--
Regards,
Sudeep