[PATCH v2 1/4] 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 unncessary to always build
it which cannot reflect the real topology on platforms have no
cluster and to avoid affecting the linux scheduling domains in the
VM. So only generate it when user specified explicitly.

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

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
 hw/acpi/aml-build.c   | 2 +-
 hw/core/machine-smp.c | 3 +++
 include/hw/boards.h   | 2 ++
 qemu-options.hx       | 2 ++
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
index e6bfac95c7..aab73af66d 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 && ms->smp.build_cluster) {
             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..5d37e8d07a 100644
--- a/hw/core/machine-smp.c
+++ b/hw/core/machine-smp.c
@@ -158,6 +158,9 @@ void machine_parse_smp_config(MachineState *ms,
     ms->smp.threads = threads;
     ms->smp.max_cpus = maxcpus;
 
+    if (config->has_clusters)
+        ms->smp.build_cluster = true;
+
     /* 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..c53f047b90 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -305,6 +305,7 @@ typedef struct DeviceMemoryState {
  * @cores: the number of cores in one cluster
  * @threads: the number of threads in one core
  * @max_cpus: the maximum number of logical processors on the machine
+ * @build_cluster: build cluster topology or not
  */
 typedef struct CpuTopology {
     unsigned int cpus;
@@ -314,6 +315,7 @@ typedef struct CpuTopology {
     unsigned int cores;
     unsigned int threads;
     unsigned int max_cpus;
+    bool build_cluster;
 } CpuTopology;
 
 /**
diff --git a/qemu-options.hx b/qemu-options.hx
index eb38e5dc40..0a710e7be3 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -342,6 +342,8 @@ SRST
     were preferred over threads), however, this behaviour is considered
     liable to change. Prior to 6.2 the preference was sockets over cores
     over threads. Since 6.2 the preference is cores over sockets over threads.
+    The cluster topology will only be generated if explicitly specified
+    by the "-cluster" option.
 
     For example, the following option defines a machine board with 2 sockets
     of 1 core before 6.2 and 1 socket of 2 cores after 6.2:
-- 
2.24.0