[PATCH 3.16 123/233] powerpc/numa: Fix percpu allocations to be NUMA aware

[Ben Hutchings]

3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

commit ba4a648f12f4cd0a8003dd229b6ca8a53348ee4b upstream.

In commit 8c272261194d ("powerpc/numa: Enable USE_PERCPU_NUMA_NODE_ID"), we
switched to the generic implementation of cpu_to_node(), which uses a percpu
variable to hold the NUMA node for each CPU.

Unfortunately we neglected to notice that we use cpu_to_node() in the allocation
of our percpu areas, leading to a chicken and egg problem. In practice what
happens is when we are setting up the percpu areas, cpu_to_node() reports that
all CPUs are on node 0, so we allocate all percpu areas on node 0.

This is visible in the dmesg output, as all pcpu allocs being in group 0:

  pcpu-alloc: [0] 00 01 02 03 [0] 04 05 06 07
  pcpu-alloc: [0] 08 09 10 11 [0] 12 13 14 15
  pcpu-alloc: [0] 16 17 18 19 [0] 20 21 22 23
  pcpu-alloc: [0] 24 25 26 27 [0] 28 29 30 31
  pcpu-alloc: [0] 32 33 34 35 [0] 36 37 38 39
  pcpu-alloc: [0] 40 41 42 43 [0] 44 45 46 47

To fix it we need an early_cpu_to_node() which can run prior to percpu being
setup. We already have the numa_cpu_lookup_table we can use, so just plumb it
in. With the patch dmesg output shows two groups, 0 and 1:

  pcpu-alloc: [0] 00 01 02 03 [0] 04 05 06 07
  pcpu-alloc: [0] 08 09 10 11 [0] 12 13 14 15
  pcpu-alloc: [0] 16 17 18 19 [0] 20 21 22 23
  pcpu-alloc: [1] 24 25 26 27 [1] 28 29 30 31
  pcpu-alloc: [1] 32 33 34 35 [1] 36 37 38 39
  pcpu-alloc: [1] 40 41 42 43 [1] 44 45 46 47

We can also check the data_offset in the paca of various CPUs, with the fix we
see:

  CPU 0:  data_offset = 0x0ffe8b0000
  CPU 24: data_offset = 0x1ffe5b0000

And we can see from dmesg that CPU 24 has an allocation on node 1:

  node   0: [mem 0x0000000000000000-0x0000000fffffffff]
  node   1: [mem 0x0000001000000000-0x0000001fffffffff]

Fixes: 8c272261194d ("powerpc/numa: Enable USE_PERCPU_NUMA_NODE_ID")
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Reviewed-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/topology.h | 14 ++++++++++++++
 arch/powerpc/kernel/setup_64.c      |  4 ++--
 2 files changed, 16 insertions(+), 2 deletions(-)

--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -44,8 +44,22 @@ extern void __init dump_numa_cpu_topolog
 extern int sysfs_add_device_to_node(struct device *dev, int nid);
 extern void sysfs_remove_device_from_node(struct device *dev, int nid);
 
+static inline int early_cpu_to_node(int cpu)
+{
+	int nid;
+
+	nid = numa_cpu_lookup_table[cpu];
+
+	/*
+	 * Fall back to node 0 if nid is unset (it should be, except bugs).
+	 * This allows callers to safely do NODE_DATA(early_cpu_to_node(cpu)).
+	 */
+	return (nid < 0) ? 0 : nid;
+}
 #else
 
+static inline int early_cpu_to_node(int cpu) { return 0; }
+
 static inline void dump_numa_cpu_topology(void) {}
 
 static inline int sysfs_add_device_to_node(struct device *dev, int nid)
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -739,7 +739,7 @@ void ppc64_boot_msg(unsigned int src, co
 
 static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align)
 {
-	return __alloc_bootmem_node(NODE_DATA(cpu_to_node(cpu)), size, align,
+	return __alloc_bootmem_node(NODE_DATA(early_cpu_to_node(cpu)), size, align,
 				    __pa(MAX_DMA_ADDRESS));
 }
 
@@ -750,7 +750,7 @@ static void __init pcpu_fc_free(void *pt
 
 static int pcpu_cpu_distance(unsigned int from, unsigned int to)
 {
-	if (cpu_to_node(from) == cpu_to_node(to))
+	if (early_cpu_to_node(from) == early_cpu_to_node(to))
 		return LOCAL_DISTANCE;
 	else
 		return REMOTE_DISTANCE;