linux-kernel - Re: [PATCH] Assign CPUs to nodes in round-robin manner on Fake NUMA.

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Message-Id: <20101007004252.599b6888.akpm@linux-foundation.org>
Date:	Thu, 7 Oct 2010 00:42:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nikanth Karthikesan <knikanth@...e.de>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Assign CPUs to nodes in round-robin manner on Fake
 NUMA.

On Thu, 30 Sep 2010 17:34:10 +0530 Nikanth Karthikesan <knikanth@...e.de> wrote:

> Assign CPUs to nodes in round-robin manner on Fake NUMA.
> 
> commit d9c2d5ac6af87b4491bff107113aaf16f6c2b2d9
> "x86, numa: Use near(er) online node instead of roundrobin for NUMA"
> changed NUMA initialization on Intel to choose the nearest online node or
> first node. Fake NUMA would be better of with round-robin initialization,
> instead of the all CPUS on first node. Change the choice of first node, back
> to round-robin.
> 

Why would fake NUMA "be better off with round-robin initialization"?

> 
> ---
> 
> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> index 85f69cd..47dd171 100644
> --- a/arch/x86/kernel/cpu/intel.c
> +++ b/arch/x86/kernel/cpu/intel.c
> @@ -283,9 +283,7 @@ static void __cpuinit srat_detect_node(struct cpuinfo_x86 *c)
>  	/* Don't do the funky fallback heuristics the AMD version employs
>  	   for now. */
>  	node = apicid_to_node[apicid];
> -	if (node == NUMA_NO_NODE)
> -		node = first_node(node_online_map);
> -	else if (!node_online(node)) {
> +	if (node == NUMA_NO_NODE || !node_online(node)) {
>  		/* reuse the value from init_cpu_to_node() */
>  		node = cpu_to_node(cpu);
>  	}
> --
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