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, 4 insertions, 3 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index b39377de3f..fd1f8135fb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -206,13 +206,14 @@ SRST
 ERST
 
 DEF("smp", HAS_ARG, QEMU_OPTION_smp,
-    "-smp [[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,cores=cores][,threads=threads]\n"
+    "-smp [[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,clusters=clusters][,cores=cores][,threads=threads]\n"
     "                set the number of initial CPUs to 'n' [default=1]\n"
     "                maxcpus= maximum number of total CPUs, including\n"
     "                offline CPUs for hotplug, etc\n"
     "                sockets= number of sockets on the machine board\n"
     "                dies= number of dies in one socket\n"
-    "                cores= number of cores in one die\n"
+    "                clusters= number of clusters in one die\n"
+    "                cores= number of cores in one cluster\n"
     "                threads= number of threads in one core\n"
     "Note: Different machines may have different subsets of the CPU topology\n"
     "      parameters supported, so the actual meaning of the supported parameters\n"
@@ -228,7 +229,7 @@ DEF("smp", HAS_ARG, QEMU_OPTION_smp,
     "      must be set as 1 in the purpose of correct parsing.\n",
     QEMU_ARCH_ALL)
 SRST
-``-smp [[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,cores=cores][,threads=threads]``
+``-smp [[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,clusters=clusters][,cores=cores][,threads=threads]``
     Simulate a SMP system with '\ ``n``\ ' CPUs initially present on
     the machine type board. On boards supporting CPU hotplug, the optional
     '\ ``maxcpus``\ ' parameter can be set to enable further CPUs to be