Re: [PATCH x86/mm] x86-64, NUMA: Don't call numa_set_distanc() for all possible node combinations during emulation

[Yinghai Lu <yinghai@kernel.org>]

On 03/11/2011 01:31 AM, Tejun Heo wrote:
> The distance transforming in numa_emulation() used to call
> numa_set_distance() for all MAX_NUMNODES * MAX_NUMNODES node
> combinations regardless of which are enabled.  As numa_set_distance()
> ignores all out-of-bound distance settings, this doesn't cause any
> problem other than looping unnecessarily many times during boot.
> 
> However, as MAX_NUMNODES * MAX_NUMNODES can be pretty high, update the
> code such that it iterates through only the enabled combinations.
> 
> Yinghai Lu identified the issue and provided an initial patch to
> address the issue; however, the patch was incorrect in that it didn't
> build emulated distance table when there's no physical distance table
> and unnecessarily complex.
> 
>   http://thread.gmane.org/gmane.linux.kernel/1107986/focus=1107988
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Yinghai Lu <yinghai@kernel.org>
> ---
>  arch/x86/mm/numa_emulation.c |   23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/mm/numa_emulation.c b/arch/x86/mm/numa_emulation.c
> index 3696be0..ad091e4 100644
> --- a/arch/x86/mm/numa_emulation.c
> +++ b/arch/x86/mm/numa_emulation.c
> @@ -301,7 +301,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>  	const u64 max_addr = max_pfn << PAGE_SHIFT;
>  	u8 *phys_dist = NULL;
>  	size_t phys_size = numa_dist_cnt * numa_dist_cnt * sizeof(phys_dist[0]);
> -	int dfl_phys_nid;
> +	int max_emu_nid, dfl_phys_nid;
>  	int i, j, ret;
>  
>  	if (!emu_cmdline)
> @@ -358,12 +358,17 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>  					node_distance(i, j);
>  	}
>  
> -	/* determine the default phys nid to use for unmapped nodes */
> +	/*
> +	 * Determine the max emulated nid and the default phys nid to use
> +	 * for unmapped nodes.
> +	 */
> +	max_emu_nid = 0;
>  	dfl_phys_nid = NUMA_NO_NODE;
>  	for (i = 0; i < ARRAY_SIZE(emu_nid_to_phys); i++) {
>  		if (emu_nid_to_phys[i] != NUMA_NO_NODE) {
> -			dfl_phys_nid = emu_nid_to_phys[i];
> -			break;
> +			max_emu_nid = i;
> +			if (dfl_phys_nid == NUMA_NO_NODE)
> +				dfl_phys_nid = emu_nid_to_phys[i];
>  		}
>  	}
>  	if (dfl_phys_nid == NUMA_NO_NODE) {
> @@ -393,14 +398,10 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>  		if (emu_nid_to_phys[i] == NUMA_NO_NODE)
>  			emu_nid_to_phys[i] = dfl_phys_nid;
>  
> -	/*
> -	 * Transform distance table.  numa_set_distance() ignores all
> -	 * out-of-bound distances.  Just call it for every possible node
> -	 * combination.
> -	 */
> +	/* transform distance table */
>  	numa_reset_distance();
> -	for (i = 0; i < MAX_NUMNODES; i++) {
> -		for (j = 0; j < MAX_NUMNODES; j++) {
> +	for (i = 0; i < max_emu_nid + 1; i++) {
> +		for (j = 0; j < max_emu_nid + 1; j++) {

using num_emu_nids would be better?

Yinghai