hw/core/machine: Introduce CPU cluster topology support

The new Cluster-Aware Scheduling support has landed in Linux 5.16,
which has been proved to benefit the scheduling performance (e.g.
load balance and wake_affine strategy) on both x86_64 and AArch64.

So now in Linux 5.16 we have four-level arch-neutral CPU topology
definition like below and a new scheduler level for clusters.
struct cpu_topology {
    int thread_id;
    int core_id;
    int cluster_id;
    int package_id;
    int llc_id;
    cpumask_t thread_sibling;
    cpumask_t core_sibling;
    cpumask_t cluster_sibling;
    cpumask_t llc_sibling;
}

A cluster generally means a group of CPU cores which share L2 cache
or other mid-level resources, and it is the shared resources that
is used to improve scheduler's behavior. From the point of view of
the size range, it's between CPU die and CPU core. For example, on
some ARM64 Kunpeng servers, we have 6 clusters in each NUMA node,
and 4 CPU cores in each cluster. The 4 CPU cores share a separate
L2 cache and a L3 cache tag, which brings cache affinity advantage.

In virtualization, on the Hosts which have pClusters (physical
clusters), if we can design a vCPU topology with cluster level for
guest kernel and have a dedicated vCPU pinning. A Cluster-Aware
Guest kernel can also make use of the cache affinity of CPU clusters
to gain similar scheduling performance.

This patch adds infrastructure for CPU cluster level topology
configuration and parsing, so that the user can specify cluster
parameter if their machines support it.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Message-Id: <20211228092221.21068-3-wangyanan55@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[PMD: Added '(since 7.0)' to @clusters in qapi/machine.json]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 7597cec440..f49a2578ea 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -129,10 +129,12 @@ typedef struct {
  * SMPCompatProps:
  * @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
  */
 typedef struct {
     bool prefer_sockets;
     bool dies_supported;
+    bool clusters_supported;
 } SMPCompatProps;
 
 /**
@@ -299,7 +301,8 @@ typedef struct DeviceMemoryState {
  * @cpus: the number of present logical processors on the machine
  * @sockets: the number of sockets on the machine
  * @dies: the number of dies in one socket
- * @cores: the number of cores in one die
+ * @clusters: the number of clusters in one die
+ * @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
  */
@@ -307,6 +310,7 @@ typedef struct CpuTopology {
     unsigned int cpus;
     unsigned int sockets;
     unsigned int dies;
+    unsigned int clusters;
     unsigned int cores;
     unsigned int threads;
     unsigned int max_cpus;