[Qemu-devel] [RFC PATCH v3] numa: enable sparse node numbering

[Nishanth Aravamudan]

Sparse node numbering occurs on powerpc in practice under PowerVM. In
order to emulate the same NUMA topology under qemu, the assumption that
NUMA nodes are linearly ordered has to be removed. qemu actually already
supports (inasmuch as it doesn't throw an error) sparse node numbering
by the end-user, but the information is effectively ignored and the
nodes are populated linearly starting at 0. This means a user's node ID
requests are not honored in the Linux kernel, and that the topology may
not be as requested (in terms of the CPU/memory placement).

Add a present field to NodeInfo which indicates if a given nodeid was
present on the command-line or not. Current code relies on a memory
value being passed for a node to indicate presence, which is
insufficient in the presence of memoryless nodes or sparse numbering.
Adjust the iteration of various NUMA loops to use the maximum known NUMA
ID rather than the number of NUMA nodes.

numa.c::set_numa_nodes() has become a bit more convoluted for
round-robin'ing the CPUs over known nodes when not specified by the
user.

Note that architecture-specific code still possibly needs changes
(forthcoming) for both sparse node numbering and memoryless nodes. This
only puts in the generic infrastructure to support that.

Examples:

(1) qemu-system-x86_64 -enable-kvm -m 4096 -numa node,nodeid=3 -numa
node,nodeid=2 -smp 16

Before:

node 0 cpus: 0 2 4 6 8 10 12 14
node 0 size: 2048 MB
node 1 cpus: 1 3 5 7 9 11 13 15
node 1 size: 2048 MB

After:

node 2 cpus: 0 2 4 6 8 10 12 14                                               |
node 2 size: 2048 MB                                                          |
node 3 cpus: 1 3 5 7 9 11 13 15                                               |
node 3 size: 2048 MB

(2) qemu-system-x86_64 -enable-kvm -m 4096 -numa node,nodeid=0 -numa
node,nodeid=1 -numa node,nodeid=2 -numa node,nodeid=3 -smp 16

node 0 cpus: 0 4 8 12                                                         |
node 0 size: 1024 MB                                                          |
node 1 cpus: 1 5 9 13                                                         |
node 1 size: 1024 MB                                                          |
node 2 cpus: 2 6 10 14                                                        |
node 2 size: 1024 MB                                                          |
node 3 cpus: 3 7 11 15                                                        |
node 3 size: 1024 MB

(qemu) info numa
4 nodes
node 0 cpus: 0 4 8 12
node 0 size: 1024 MB
node 1 cpus: 1 5 9 13
node 1 size: 1024 MB
node 2 cpus: 2 6 10 14
node 2 size: 1024 MB
node 3 cpus: 3 7 11 15
node 3 size: 1024 MB

Signed-off-by: Nishanth Aravamudan <address@hidden>
Tested-by: Hu Tao <address@hidden>

---
Based off mst's for_upstream tag, which has the NodeInfo changes.

v1 -> v2:
  Modify set_numa_nodes loop for round-robin'ing CPUs.

v2 -> v3:
  Updated changelog to indicate problem being solved.
  Updated memory_region_allocate_system_memory based upon feedback from
    Hu.
  Updated set_numa_nodes loop again to be simpler based upon feedback
    from Hu.
  Fixed bug with a mix of nodes with nodeid specified and without, where
    the same nodeid would be used by the explicit specification and the
    auto-numbering code.

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 277230d..b90bf66 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -145,11 +145,13 @@ extern int mem_prealloc;
  */
 #define MAX_CPUMASK_BITS 255
 
-extern int nb_numa_nodes;
+extern int nb_numa_nodes; /* Number of NUMA nodes */
+extern int max_numa_node; /* Highest specified NUMA node ID */
 typedef struct node_info {
     uint64_t node_mem;
     DECLARE_BITMAP(node_cpu, MAX_CPUMASK_BITS);
     struct HostMemoryBackend *node_memdev;
+    bool present;
 } NodeInfo;
 extern NodeInfo numa_info[MAX_NODES];
 void set_numa_nodes(void);
diff --git a/monitor.c b/monitor.c
index c7f8797..4721996 100644
--- a/monitor.c
+++ b/monitor.c
@@ -2003,7 +2003,10 @@ static void do_info_numa(Monitor *mon, const QDict 
*qdict)
     CPUState *cpu;
 
     monitor_printf(mon, "%d nodes\n", nb_numa_nodes);
-    for (i = 0; i < nb_numa_nodes; i++) {
+    for (i = 0; i < max_numa_node; i++) {
+        if (!numa_info[i].present) {
+            continue;
+        }
         monitor_printf(mon, "node %d cpus:", i);
         CPU_FOREACH(cpu) {
             if (cpu->numa_node == i) {
diff --git a/numa.c b/numa.c
index e471afe..d6b86ab 100644
--- a/numa.c
+++ b/numa.c
@@ -53,7 +53,10 @@ static void numa_node_parse(NumaNodeOptions *node, QemuOpts 
*opts, Error **errp)
     if (node->has_nodeid) {
         nodenr = node->nodeid;
     } else {
-        nodenr = nb_numa_nodes;
+        nodenr = 0;
+        while (numa_info[nodenr].present) {
+            nodenr++;
+        }
     }
 
     if (nodenr >= MAX_NODES) {
@@ -106,6 +109,10 @@ static void numa_node_parse(NumaNodeOptions *node, 
QemuOpts *opts, Error **errp)
         numa_info[nodenr].node_mem = object_property_get_int(o, "size", NULL);
         numa_info[nodenr].node_memdev = MEMORY_BACKEND(o);
     }
+    numa_info[nodenr].present = true;
+    if (nodenr >= max_numa_node) {
+        max_numa_node = nodenr + 1;
+    }
 }
 
 int numa_init_func(QemuOpts *opts, void *opaque)
@@ -155,7 +162,7 @@ void set_numa_nodes(void)
 {
     if (nb_numa_nodes > 0) {
         uint64_t numa_total;
-        int i;
+        int i, j = -1;
 
         if (nb_numa_nodes > MAX_NODES) {
             nb_numa_nodes = MAX_NODES;
@@ -164,27 +171,29 @@ void set_numa_nodes(void)
         /* If no memory size if given for any node, assume the default case
          * and distribute the available memory equally across all nodes
          */
-        for (i = 0; i < nb_numa_nodes; i++) {
-            if (numa_info[i].node_mem != 0) {
+        for (i = 0; i < max_numa_node; i++) {
+            if (numa_info[i].present && numa_info[i].node_mem != 0) {
                 break;
             }
         }
-        if (i == nb_numa_nodes) {
+        if (i == max_numa_node) {
             uint64_t usedmem = 0;
 
             /* On Linux, the each node's border has to be 8MB aligned,
              * the final node gets the rest.
              */
-            for (i = 0; i < nb_numa_nodes - 1; i++) {
-                numa_info[i].node_mem = (ram_size / nb_numa_nodes) &
-                                        ~((1 << 23UL) - 1);
-                usedmem += numa_info[i].node_mem;
+            for (i = 0; i < max_numa_node - 1; i++) {
+                if (numa_info[i].present) {
+                    numa_info[i].node_mem = (ram_size / nb_numa_nodes) &
+                                            ~((1 << 23UL) - 1);
+                    usedmem += numa_info[i].node_mem;
+                }
             }
             numa_info[i].node_mem = ram_size - usedmem;
         }
 
         numa_total = 0;
-        for (i = 0; i < nb_numa_nodes; i++) {
+        for (i = 0; i < max_numa_node; i++) {
             numa_total += numa_info[i].node_mem;
         }
         if (numa_total != ram_size) {
@@ -194,8 +203,9 @@ void set_numa_nodes(void)
             exit(1);
         }
 
-        for (i = 0; i < nb_numa_nodes; i++) {
-            if (!bitmap_empty(numa_info[i].node_cpu, MAX_CPUMASK_BITS)) {
+        for (i = 0; i < max_numa_node; i++) {
+            if (numa_info[i].present &&
+                !bitmap_empty(numa_info[i].node_cpu, MAX_CPUMASK_BITS)) {
                 break;
             }
         }
@@ -203,9 +213,12 @@ void set_numa_nodes(void)
          * must cope with this anyway, because there are BIOSes out there in
          * real machines which also use this scheme.
          */
-        if (i == nb_numa_nodes) {
+        if (i == max_numa_node) {
             for (i = 0; i < max_cpus; i++) {
-                set_bit(i, numa_info[i % nb_numa_nodes].node_cpu);
+                do {
+                    j = (j + 1) % max_numa_node;
+                } while (!numa_info[j].present);
+                set_bit(i, numa_info[j].node_cpu);
             }
         }
     }
@@ -217,8 +230,9 @@ void set_numa_modes(void)
     int i;
 
     CPU_FOREACH(cpu) {
-        for (i = 0; i < nb_numa_nodes; i++) {
-            if (test_bit(cpu->cpu_index, numa_info[i].node_cpu)) {
+        for (i = 0; i < max_numa_node; i++) {
+            if (numa_info[i].present &&
+                test_bit(cpu->cpu_index, numa_info[i].node_cpu)) {
                 cpu->numa_node = i;
             }
         }
@@ -266,10 +280,13 @@ void memory_region_allocate_system_memory(MemoryRegion 
*mr, Object *owner,
     }
 
     memory_region_init(mr, owner, name, ram_size);
-    for (i = 0; i < MAX_NODES; i++) {
+    for (i = 0; i < max_numa_node; i++) {
         Error *local_err = NULL;
         uint64_t size = numa_info[i].node_mem;
         HostMemoryBackend *backend = numa_info[i].node_memdev;
+        if (!numa_info[i].present) {
+            continue;
+        }
         if (!backend) {
             continue;
         }
diff --git a/vl.c b/vl.c
index 54b4627..e1a6ab8 100644
--- a/vl.c
+++ b/vl.c
@@ -195,6 +195,7 @@ static QTAILQ_HEAD(, FWBootEntry) fw_boot_order =
     QTAILQ_HEAD_INITIALIZER(fw_boot_order);
 
 int nb_numa_nodes;
+int max_numa_node;
 NodeInfo numa_info[MAX_NODES];
 
 uint8_t qemu_uuid[16];
@@ -2967,10 +2968,12 @@ int main(int argc, char **argv, char **envp)
 
     for (i = 0; i < MAX_NODES; i++) {
         numa_info[i].node_mem = 0;
+        numa_info[i].present = false;
         bitmap_zero(numa_info[i].node_cpu, MAX_CPUMASK_BITS);
     }
 
     nb_numa_nodes = 0;
+    max_numa_node = -1;
     nb_nics = 0;
 
     bdrv_init_with_whitelist();