[PATCH v4 2/6] hw/acpi/aml-build: Only generate cluster node in PPTT when specified

[Yicong Yang]

From: Yicong Yang <yangyicong@hisilicon.com>

Currently we'll always generate a cluster node no matter user has
specified '-smp clusters=X' or not. Cluster is an optional level
and will participant the building of Linux scheduling domains and
only appears on a few platforms. It's unnecessary to always build
it when it cannot reflect the real topology on platforms having no
cluster implementation. So only generate the cluster topology in
ACPI PPTT when the user has specified it explicitly in -smp.

Tested qemu-system-aarch64 with `-smp 8` and linux 6.1-rc1, without
this patch:
estuary:/sys/devices/system/cpu/cpu0/topology$ cat cluster_*
ff      # cluster_cpus
0-7     # cluster_cpus_list
56      # cluster_id

with this patch:
estuary:/sys/devices/system/cpu/cpu0/topology$ cat cluster_*
ff      # cluster_cpus
0-7     # cluster_cpus_list
36      # cluster_id, with no cluster node kernel will make it to
          physical package id

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
 hw/acpi/aml-build.c   | 2 +-
 hw/core/machine-smp.c | 2 ++
 include/hw/boards.h   | 3 +++
 qemu-options.hx       | 3 +++
 4 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index e6bfac95c7..60c1acf3da 100644
--- a/hw/acpi/aml-build.c
+++ b/hw/acpi/aml-build.c
@@ -2030,7 +2030,7 @@ void build_pptt(GArray *table_data, BIOSLinker *linker, 
MachineState *ms,
                 0, socket_id, NULL, 0);
         }
 
-        if (mc->smp_props.clusters_supported) {
+        if (mc->smp_props.clusters_supported && mc->smp_props.has_clusters) {
             if (cpus->cpus[n].props.cluster_id != cluster_id) {
                 assert(cpus->cpus[n].props.cluster_id > cluster_id);
                 cluster_id = cpus->cpus[n].props.cluster_id;
diff --git a/hw/core/machine-smp.c b/hw/core/machine-smp.c
index b39ed21e65..c3dab007da 100644
--- a/hw/core/machine-smp.c
+++ b/hw/core/machine-smp.c
@@ -158,6 +158,8 @@ void machine_parse_smp_config(MachineState *ms,
     ms->smp.threads = threads;
     ms->smp.max_cpus = maxcpus;
 
+    mc->smp_props.has_clusters = config->has_clusters;
+
     /* sanity-check of the computed topology */
     if (sockets * dies * clusters * cores * threads != maxcpus) {
         g_autofree char *topo_msg = cpu_hierarchy_to_string(ms);
diff --git a/include/hw/boards.h b/include/hw/boards.h
index 311ed17e18..06ed66453f 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -130,11 +130,14 @@ typedef struct {
  * @prefer_sockets - whether sockets are preferred over cores in smp parsing
  * @dies_supported - whether dies are supported by the machine
  * @clusters_supported - whether clusters are supported by the machine
+ * @has_clusters - whether clusters are explicitly specified in the user
+ *                 provided SMP configuration
  */
 typedef struct {
     bool prefer_sockets;
     bool dies_supported;
     bool clusters_supported;
+    bool has_clusters;
 } SMPCompatProps;
 
 /**
diff --git a/qemu-options.hx b/qemu-options.hx
index eb38e5dc40..bbdbdef0af 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -349,6 +349,9 @@ SRST
     ::
 
         -smp 2
+
+    Note: The cluster topology will only be generated in ACPI and exposed
+    to guest if it's explicitly specified in -smp.
 ERST
 
 DEF("numa", HAS_ARG, QEMU_OPTION_numa,
-- 
2.24.0