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    Subject[tip:x86/mm] x86, numa: Use near(er) online node instead of roundrobin for NUMA
    Commit-ID:  d9c2d5ac6af87b4491bff107113aaf16f6c2b2d9
    Gitweb: http://git.kernel.org/tip/d9c2d5ac6af87b4491bff107113aaf16f6c2b2d9
    Author: Yinghai Lu <yinghai@kernel.org>
    AuthorDate: Sat, 21 Nov 2009 00:23:37 -0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Mon, 23 Nov 2009 10:06:24 +0100

    x86, numa: Use near(er) online node instead of roundrobin for NUMA

    CPU to node mapping is set via the following sequence:

    1. numa_init_array(): Set up roundrobin from cpu to online node

    2. init_cpu_to_node(): Set that according to apicid_to_node[]
    according to srat only handle the node that
    is online, and leave other cpu on node
    without ram (aka not online) to still
    roundrobin.

    3. later call srat_detect_node for Intel/AMD, will use first_online
    node or nearby node.

    Problem is that setup_per_cpu_areas() is not called between 2 and 3,
    the per_cpu for cpu on node with ram is on different node, and could
    put that on node with two hops away.

    So try to optimize this and add find_near_online_node() and call
    init_cpu_to_node().

    Signed-off-by: Yinghai Lu <yinghai@kernel.org>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    LKML-Reference: <4B07A739.3030104@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/kernel/cpu/intel.c | 6 +++++-
    arch/x86/mm/numa_64.c | 21 ++++++++++++++++++++-
    2 files changed, 25 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
    index 40e1835..c900b73 100644
    --- a/arch/x86/kernel/cpu/intel.c
    +++ b/arch/x86/kernel/cpu/intel.c
    @@ -263,8 +263,12 @@ 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_online(node))
    + if (node == NUMA_NO_NODE)
    node = first_node(node_online_map);
    + else if (!node_online(node)) {
    + /* reuse the value from init_cpu_to_node() */
    + node = cpu_to_node(cpu);
    + }
    numa_set_node(cpu, node);

    printk(KERN_INFO "CPU %d/0x%x -> Node %d\n", cpu, apicid, node);
    diff --git a/arch/x86/mm/numa_64.c b/arch/x86/mm/numa_64.c
    index 3acd870..83bbc70 100644
    --- a/arch/x86/mm/numa_64.c
    +++ b/arch/x86/mm/numa_64.c
    @@ -764,6 +764,25 @@ static __init int numa_setup(char *opt)
    early_param("numa", numa_setup);

    #ifdef CONFIG_NUMA
    +
    +static __init int find_near_online_node(int node)
    +{
    + int n, val;
    + int min_val = INT_MAX;
    + int best_node = -1;
    +
    + for_each_online_node(n) {
    + val = node_distance(node, n);
    +
    + if (val < min_val) {
    + min_val = val;
    + best_node = n;
    + }
    + }
    +
    + return best_node;
    +}
    +
    /*
    * Setup early cpu_to_node.
    *
    @@ -795,7 +814,7 @@ void __init init_cpu_to_node(void)
    if (node == NUMA_NO_NODE)
    continue;
    if (!node_online(node))
    - continue;
    + node = find_near_online_node(node);
    numa_set_node(cpu, node);
    }
    }

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