linux-kernel - Re: [PATCH v10 2/6] x86: Support Generic Initiator only proximity domains

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Date:   Fri, 25 Sep 2020 18:08:17 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     linux-mm@...ck.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        rafael@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        linuxarm@...wei.com, Dan Williams <dan.j.williams@...el.com>,
        Brice Goglin <Brice.Goglin@...ia.fr>,
        Sean V Kelley <sean.v.kelley@...ux.intel.com>,
        linux-api@...r.kernel.org, Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [PATCH v10 2/6] x86: Support Generic Initiator only proximity
 domains

On Fri, Sep 25, 2020 at 12:32:26PM +0100, Jonathan Cameron wrote:
> I don't think we can.  This is doing the same operation as
> is done for memoryless cpu nodes in the init_cpu_to_node() call above
> so it would make little sense from a code flow point of view, even if
> it were possible.  However it isn't possible as far as I can see.
> 
> It is called after init_cpu_to_node() because...
> * A GI node may also be a CPU node and / or a Memory Node, but we only
>   have to do anything extra if it has neither of these.
>   Easiest way to do that is use the same logic init_cpu_to_node() 
>   does and rely on ordering wrt to the other two types of nodes that
>   have already been handled.  We could have could just call it at the
>   end of init_cpu_to_node() but I'd not be happy doing so without renaming
>   that function and then we'd end up with a horrible name like
>   init_cpu_to_node_and_gi() as they are rather different things.
> 
> It needs to happen before use is made of the node_data which is allocated
> in init_gi_nodes() / init_memoryless_node() / alloc_node_data()

Let's put the gist of this requirement in the comment above
init_gi_nodes() for future reference.

...

> It might be possible to allocate the zonelists for this special case later
> in the boot flow, but it seems like we would be adding a lot of complexity
> to avoid a single function call.

Nah, probably not worth the hassle.

> How about this?
> 
> +/*
> + * A node may exist which has one or more Generic Initiators but no
> + * CPUs and no memory.
> + * When this function is called, any nodes containing either memory
> + * and/or CPUs will already be online and there is no need to do
> + * anything extra, even if they also contain one or more Generic
> + * Initiators.
> + */

Yes, along with the above gist.

Thx!

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette