linux-kernel - Re: [PATCH] Fake NUMA emulation for PowerPC (Take 2)

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Message-Id: <1200635703.18783.5.camel@concordia.ozlabs.ibm.com>
Date:	Fri, 18 Jan 2008 16:55:03 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	linuxppc-dev@...abs.org, LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] Fake NUMA emulation for PowerPC (Take 2)

On Sat, 2007-12-08 at 04:07 +0530, Balbir Singh wrote:
> Here's a dumb simple implementation of fake NUMA nodes for PowerPC. Fake
> NUMA nodes can be specified using the following command line option
> 

> 
> Comments are as always welcome!

Here's some :)

> diff -puN arch/powerpc/mm/numa.c~ppc-fake-numa-easy arch/powerpc/mm/numa.c
> --- linux-2.6.24-rc4-mm1/arch/powerpc/mm/numa.c~ppc-fake-numa-easy	2007-12-07 21:25:55.000000000 +0530
> +++ linux-2.6.24-rc4-mm1-balbir/arch/powerpc/mm/numa.c	2007-12-08 03:19:46.000000000 +0530
> @@ -24,6 +24,8 @@
>  
>  static int numa_enabled = 1;
>  
> +static char *cmdline __initdata;

Can you call this fake_numa_args or something, cmdline is a bit generic.


> @@ -39,6 +41,43 @@ static bootmem_data_t __initdata plat_no
>  static int min_common_depth;
>  static int n_mem_addr_cells, n_mem_size_cells;
>  
> +static int __cpuinit fake_numa_create_new_node(unsigned long end_pfn,
> +						unsigned int *nid)
> +{
> +	unsigned long long mem;
> +	char *p = cmdline;
> +	static unsigned int fake_nid = 0;
> +	static unsigned long long curr_boundary = 0;
> +
> +	*nid = fake_nid;

As I mentioned in my other email I think this is broken, you
unconditionally overwrite *nid, even if no fake numa was specified?

> +	if (!p)
> +		return 0;
> +
> +	mem = memparse(p, &p);
> +	if (!mem)
> +		return 0;
> +
> +	if (mem < curr_boundary)
> +		return 0;
> +
> +	curr_boundary = mem;
> +
> +	if ((end_pfn << PAGE_SHIFT) > mem) {
> +		/*
> +		 * Skip commas and spaces
> +		 */
> +		while (*p == ',' || *p == ' ' || *p == '\t')
> +			p++;
> +
> +		cmdline = p;
> +		fake_nid++;
> +		*nid = fake_nid;
> +		dbg("created new fake_node with id %d\n", fake_nid);
> +		return 1;
> +	}
> +	return 0;
> +}
> +
>  static void __cpuinit map_cpu_to_node(int cpu, int node)
>  {
>  	numa_cpu_lookup_table[cpu] = node;
> @@ -344,12 +383,14 @@ static void __init parse_drconf_memory(s
>  			if (nid == 0xffff || nid >= MAX_NUMNODES)
>  				nid = default_nid;
>  		}
> -		node_set_online(nid);
>  
>  		size = numa_enforce_memory_limit(start, lmb_size);
>  		if (!size)
>  			continue;
>  
> +		fake_numa_create_new_node(((start + size) >> PAGE_SHIFT), &nid);
> +		node_set_online(nid);

I can't convince myself that this is 100% ok, the moving of
node_set_online(). At the very least it's a change in behaviour,
previously we would online the node regardless of the memory limit.

>  		add_active_range(nid, start >> PAGE_SHIFT,
>  				 (start >> PAGE_SHIFT) + (size >> PAGE_SHIFT));
>  	}
> @@ -429,7 +470,6 @@ new_range:
>  		nid = of_node_to_nid_single(memory);
>  		if (nid < 0)
>  			nid = default_nid;
> -		node_set_online(nid);
>  
>  		if (!(size = numa_enforce_memory_limit(start, size))) {
>  			if (--ranges)
> @@ -438,6 +478,9 @@ new_range:
>  				continue;
>  		}
>  
> +		fake_numa_create_new_node(((start + size) >> PAGE_SHIFT), &nid);
> +		node_set_online(nid);

Ditto previous comment.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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