[Qemu-devel] [PATCH v2] x86: Allow to set NUMA distance for different NUMA nodes

[He Chen]

Current, QEMU does not provide a clear command to set vNUMA distance for
guest although we already have `-numa` command to set vNUMA nodes.

vNUMA distance makes sense in certain scenario.
But now, if we create a guest that has 4 vNUMA nodes, when we check NUMA
info via `numactl -H`, we will see:

node distance:
node    0    1    2    3
  0:   10   20   20   20
  1:   20   10   20   20
  2:   20   20   10   20
  3:   20   20   20   10

Guest kernel regards all local node as distance 10, and all remote node
as distance 20 when there is no SLIT table since QEMU doesn't build it.
It looks like a little strange when you have seen the distance in an
actual physical machine that contains 4 NUMA nodes. My machine shows:

node distance:
node    0    1    2    3
  0:   10   21   31   41
  1:   21   10   21   31
  2:   31   21   10   21
  3:   41   31   21   10

To set vNUMA distance, guest should see a complete SLIT table.
I found QEMU has provide `-acpitable` command that allows users to add
a ACPI table into guest, but it requires users building ACPI table by
themselves first. Using `-acpitable` to add a SLIT table may be not so
straightforward or flexible, imagine that when the vNUMA configuration
is changes and we need to generate another SLIT table manually. It may
not be friendly to users or upper software like libvirt.

This patch is going to add SLIT table support in QEMU, and provides
additional option `dist` for command `-numa` to allow user set vNUMA
distance by QEMU command.

With this patch, when a user wants to create a guest that contains
several vNUMA nodes and also wants to set distance among those nodes,
the QEMU command would like:

```
-object 
memory-backend-ram,size=1G,prealloc=yes,host-nodes=0,policy=bind,id=node0 \
-numa node,nodeid=0,cpus=0,memdev=node0 \
-object 
memory-backend-ram,size=1G,prealloc=yes,host-nodes=1,policy=bind,id=node1 \
-numa node,nodeid=1,cpus=1,memdev=node1 \
-object 
memory-backend-ram,size=1G,prealloc=yes,host-nodes=2,policy=bind,id=node2 \
-numa node,nodeid=2,cpus=2,memdev=node2 \
-object 
memory-backend-ram,size=1G,prealloc=yes,host-nodes=3,policy=bind,id=node3 \
-numa node,nodeid=3,cpus=3,memdev=node3 \
-numa dist,src=0,dst=1,val=21 \
-numa dist,src=0,dst=2,val=31 \
-numa dist,src=0,dst=3,val=41 \
-numa dist,src=1,dst=0,val=21 \
...
```

Signed-off-by: He Chen <address@hidden>
---
 hw/i386/acpi-build.c    | 27 +++++++++++++++++++++++++++
 include/sysemu/numa.h   |  1 +
 include/sysemu/sysemu.h |  3 +++
 numa.c                  | 44 ++++++++++++++++++++++++++++++++++++++++++++
 qapi-schema.json        | 24 ++++++++++++++++++++++--
 qemu-options.hx         | 12 +++++++++++-
 6 files changed, 108 insertions(+), 3 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 2073108..50906b9 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -2395,6 +2395,31 @@ build_srat(GArray *table_data, BIOSLinker *linker, 
MachineState *machine)
                  table_data->len - srat_start, 1, NULL, NULL);
 }
 
+/*
+ * ACPI spec 5.2.17 System Locality Distance Information Table
+ * (Revision 2.0 or later)
+ */
+static void
+build_slit(GArray *table_data, BIOSLinker *linker, MachineState *machine)
+{
+    int slit_start, i, j;
+    slit_start = table_data->len;
+
+    acpi_data_push(table_data, sizeof(AcpiTableHeader));
+
+    build_append_int_noprefix(table_data, nb_numa_nodes, 8);
+    for (i = 0; i < nb_numa_nodes; i++) {
+        for (j = 0; j < nb_numa_nodes; j++) {
+            build_append_int_noprefix(table_data, numa_info[i].distance[j], 1);
+        }
+    }
+
+    build_header(linker, table_data,
+                 (void *)(table_data->data + slit_start),
+                 "SLIT",
+                 table_data->len - slit_start, 1, NULL, NULL);
+}
+
 static void
 build_mcfg_q35(GArray *table_data, BIOSLinker *linker, AcpiMcfgInfo *info)
 {
@@ -2678,6 +2703,8 @@ void acpi_build(AcpiBuildTables *tables, MachineState 
*machine)
     if (pcms->numa_nodes) {
         acpi_add_table(table_offsets, tables_blob);
         build_srat(tables_blob, tables->linker, machine);
+        acpi_add_table(table_offsets, tables_blob);
+        build_slit(tables_blob, tables->linker, machine);
     }
     if (acpi_get_mcfg(&mcfg)) {
         acpi_add_table(table_offsets, tables_blob);
diff --git a/include/sysemu/numa.h b/include/sysemu/numa.h
index 8f09dcf..2f7a941 100644
--- a/include/sysemu/numa.h
+++ b/include/sysemu/numa.h
@@ -21,6 +21,7 @@ typedef struct node_info {
     struct HostMemoryBackend *node_memdev;
     bool present;
     QLIST_HEAD(, numa_addr_range) addr; /* List to store address ranges */
+    uint8_t distance[MAX_NODES];
 } NodeInfo;
 
 extern NodeInfo numa_info[MAX_NODES];
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 576c7ce..d674287 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -169,6 +169,9 @@ extern int mem_prealloc;
 
 #define MAX_NODES 128
 #define NUMA_NODE_UNASSIGNED MAX_NODES
+#define MIN_NUMA_DISTANCE 10
+#define DEF_NUMA_DISTANCE 20
+#define MAX_NUMA_DISTANCE 255
 
 #define MAX_OPTION_ROMS 16
 typedef struct QEMUOptionRom {
diff --git a/numa.c b/numa.c
index e01cb54..9b28e47 100644
--- a/numa.c
+++ b/numa.c
@@ -212,6 +212,28 @@ static void numa_node_parse(NumaNodeOptions *node, 
QemuOpts *opts, Error **errp)
     max_numa_nodeid = MAX(max_numa_nodeid, nodenr + 1);
 }
 
+static void numa_distance_parse(NumaDistOptions *dist, QemuOpts *opts, Error 
**errp)
+{
+    uint64_t src = dist->src;
+    uint64_t dst = dist->dst;
+    uint8_t val = dist->val;
+
+    if (src >= MAX_NODES || dst >= MAX_NODES) {
+        error_setg(errp, "Max number of NUMA nodes reached: %"
+                   PRIu64 "", src > dst ? src : dst);
+        return;
+    }
+
+    if (val < MIN_NUMA_DISTANCE) {
+        error_setg(errp,
+                "NUMA distance (%" PRIu8 ") out of range (%d) ~ (%d)",
+                dist->val, MAX_NUMA_DISTANCE, MIN_NUMA_DISTANCE);
+        return;
+    }
+
+    numa_info[src].distance[dst] = val;
+}
+
 static int parse_numa(void *opaque, QemuOpts *opts, Error **errp)
 {
     NumaOptions *object = NULL;
@@ -235,6 +257,12 @@ static int parse_numa(void *opaque, QemuOpts *opts, Error 
**errp)
         }
         nb_numa_nodes++;
         break;
+    case NUMA_OPTIONS_TYPE_DIST:
+        numa_distance_parse(&object->u.dist, opts, &err);
+        if (err) {
+            goto end;
+        }
+        break;
     default:
         abort();
     }
@@ -294,6 +322,21 @@ static void validate_numa_cpus(void)
     g_free(seen_cpus);
 }
 
+static void default_numa_distance(void)
+{
+    int i, j;
+
+    for (i = 0; i < nb_numa_nodes; i++) {
+        for (j = 0; j < nb_numa_nodes; j++) {
+            if (i == j && numa_info[i].distance[j] != MIN_NUMA_DISTANCE) {
+                numa_info[i].distance[j] = MIN_NUMA_DISTANCE;
+            } else if (numa_info[i].distance[j] <= MIN_NUMA_DISTANCE) {
+                numa_info[i].distance[j] = DEF_NUMA_DISTANCE;
+            }
+        }
+    }
+}
+
 void parse_numa_opts(MachineClass *mc)
 {
     int i;
@@ -390,6 +433,7 @@ void parse_numa_opts(MachineClass *mc)
         }
 
         validate_numa_cpus();
+        default_numa_distance();
     } else {
         numa_set_mem_node_id(0, ram_size, 0);
     }
diff --git a/qapi-schema.json b/qapi-schema.json
index 32b4a4b..cbb7176 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -5647,7 +5647,7 @@
 # Since: 2.1
 ##
 { 'enum': 'NumaOptionsType',
-  'data': [ 'node' ] }
+  'data': [ 'node', 'dist' ] }
 
 ##
 # @NumaOptions:
@@ -5660,7 +5660,8 @@
   'base': { 'type': 'NumaOptionsType' },
   'discriminator': 'type',
   'data': {
-    'node': 'NumaNodeOptions' }}
+    'node': 'NumaNodeOptions',
+    'dist': 'NumaDistOptions' }}
 
 ##
 # @NumaNodeOptions:
@@ -5689,6 +5690,25 @@
    '*memdev': 'str' }}
 
 ##
+# @NumaDistOptions:
+#
+# Set distance between 2 NUMA nodes. (for OptsVisitor)
+#
+# @src: source NUMA node.
+#
+# @dst: destination NUMA node.
+#
+# @val: NUMA distance from source node to destination node.
+#
+# Since: 2.10
+##
+{ 'struct': 'NumaDistOptions',
+  'data': {
+   'src': 'uint64',
+   'dst': 'uint64',
+   'val': 'uint8' }}
+
+##
 # @HostMemPolicy:
 #
 # Host memory policy types
diff --git a/qemu-options.hx b/qemu-options.hx
index 8dd8ee3..b7b4ec5 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -139,12 +139,15 @@ ETEXI
 
 DEF("numa", HAS_ARG, QEMU_OPTION_numa,
     "-numa node[,mem=size][,cpus=firstcpu[-lastcpu]][,nodeid=node]\n"
-    "-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node]\n", 
QEMU_ARCH_ALL)
+    "-numa node[,memdev=id][,cpus=firstcpu[-lastcpu]][,nodeid=node]\n"
+    "-numa dist,src=source,dst=destination,val=distance\n", QEMU_ARCH_I386)
 STEXI
 @item -numa node[,address@hidden,address@hidden@var{lastcpu}]][,address@hidden
 @itemx -numa node[,address@hidden,address@hidden@var{lastcpu}]][,address@hidden
address@hidden -numa dist,address@hidden,address@hidden,address@hidden
 @findex -numa
 Define a NUMA node and assign RAM and VCPUs to it.
+Set NUMA distance from source node to destination node.
 
 @var{firstcpu} and @var{lastcpu} are CPU indexes. Each
 @samp{cpus} option represent a contiguous range of CPU indexes
@@ -167,6 +170,13 @@ split equally between them.
 @samp{mem} and @samp{memdev} are mutually exclusive. Furthermore,
 if one node uses @samp{memdev}, all of them have to use it.
 
address@hidden and @var{destination} are NUMA node ID.
address@hidden is NUMA distance from @var{source} to @var{destination}.
+The distance from node A to node B may be different from the distance from
+node B to node A since the distance allows to be asymmetry.
+If the distance is not set, the default distance for local NUMA node is 10,
+and 20 for remote node.
+
 Note that the address@hidden option doesn't allocate any of the
 specified resources, it just assigns existing resources to NUMA
 nodes. This means that one still has to use the @option{-m},
-- 
2.7.4