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

From: Borislav Petkov <bp@alien8.de>
To: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	linux-acpi@vger.kernel.org, rafael@kernel.org,
	linux-api@vger.kernel.org, x86@kernel.org,
	Hanjun Guo <guohanjun@huawei.com>,
	linux-kernel@vger.kernel.org, linuxarm@huawei.com,
	linux-mm@kvack.org, Ingo Molnar <mingo@redhat.com>,
	Brice Goglin <Brice.Goglin@inria.fr>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Dan Williams <dan.j.williams@intel.com>,
	linux-arm-kernel@lists.infradead.org,
	Sean V Kelley <sean.v.kelley@linux.intel.com>
Subject: Re: [PATCH v10 2/6] x86: Support Generic Initiator only proximity domains
Date: Fri, 25 Sep 2020 18:08:17 +0200	[thread overview]
Message-ID: <20200925160817.GJ16872@zn.tnic> (raw)
In-Reply-To: <20200925123226.0000636a@Huawei.com>

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

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