[RFC PATCH v3 1/4] vl.c: Add -smp, clusters=* command line support for ARM cpu

[Yanan Wang]

In implementations of ARM architecture, at most there could be a
cpu hierarchy like "sockets/dies/clusters/cores/threads" defined.
For example, ARM64 server chip Kunpeng 920 totally has 2 sockets,
2 NUMA nodes (also means cpu dies) in each socket, 6 clusters in
each NUMA node, 4 cores in each cluster, and doesn't support SMT.
Clusters within the same NUMA share a L3 cache and cores within
the same cluster share a L2 cache.

The cache affinity of ARM cluster has been proved to improve the
kernel scheduling performance and a patchset has been posted, in
which a general sched_domain for clusters was added and a cluster
level was added in the arch-neutral cpu topology struct like below.

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;
}

In virtuallization, exposing the cluster level topology to guest
kernel may also improve the scheduling performance. So let's add
the -smp, clusters=* command line support for ARM cpu, then users
will be able to define a four-level cpu hierarchy for machines
and it will be sockets/clusters/cores/threads.

Because we only support clusters for ARM cpu currently, a new member
"smp_clusters" is only added to the VirtMachineState structure.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
 include/hw/arm/virt.h |  1 +
 qemu-options.hx       | 26 +++++++++++++++-----------
 softmmu/vl.c          |  3 +++
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index f546dd2023..74fff9667b 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -156,6 +156,7 @@ struct VirtMachineState {
     char *pciehb_nodename;
     const int *irqmap;
     int fdt_size;
+    unsigned smp_clusters;
     uint32_t clock_phandle;
     uint32_t gic_phandle;
     uint32_t msi_phandle;
diff --git a/qemu-options.hx b/qemu-options.hx
index bd97086c21..245eb415a6 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -184,25 +184,29 @@ SRST
 ERST
 
 DEF("smp", HAS_ARG, QEMU_OPTION_smp,
-    "-smp 
[cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,dies=dies][,sockets=sockets]\n"
+    "-smp 
[cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,clusters=clusters][,dies=dies][,sockets=sockets]\n"
     "                set the number of CPUs to 'n' [default=1]\n"
     "                maxcpus= maximum number of total cpus, including\n"
     "                offline CPUs for hotplug, etc\n"
-    "                cores= number of CPU cores on one socket (for PC, it's on 
one die)\n"
+    "                cores= number of CPU cores on one socket\n"
+    "                (it's on one die for PC, and on one cluster for ARM)\n"
     "                threads= number of threads on one CPU core\n"
+    "                clusters= number of CPU clusters on one socket (for ARM 
only)\n"
     "                dies= number of CPU dies on one socket (for PC only)\n"
     "                sockets= number of discrete sockets in the system\n",
         QEMU_ARCH_ALL)
 SRST
-``-smp 
[cpus=]n[,cores=cores][,threads=threads][,dies=dies][,sockets=sockets][,maxcpus=maxcpus]``
-    Simulate an SMP system with n CPUs. On the PC target, up to 255 CPUs
-    are supported. On Sparc32 target, Linux limits the number of usable
-    CPUs to 4. For the PC target, the number of cores per die, the
-    number of threads per cores, the number of dies per packages and the
-    total number of sockets can be specified. Missing values will be
-    computed. If any on the three values is given, the total number of
-    CPUs n can be omitted. maxcpus specifies the maximum number of
-    hotpluggable CPUs.
+``-smp 
[cpus=]n[,cores=cores][,threads=threads][,clusters=clusters][,dies=dies][,sockets=sockets][,maxcpus=maxcpus]``
+    Simulate an SMP system with n CPUs. On the PC target, up to 255
+    CPUs are supported. On the Sparc32 target, Linux limits the number
+    of usable CPUs to 4. For the PC target, the number of threads per
+    core, the number of cores per die, the number of dies per package
+    and the total number of sockets can be specified. For the ARM target,
+    the number of threads per core, the number of cores per cluster, the
+    number of clusters per socket and the total number of sockets can be
+    specified. And missing values will be computed. If any of the five
+    values is given, the total number of CPUs n can be omitted. Maxcpus
+    specifies the maximum number of hotpluggable CPUs.
 
     For the ARM target, at least one of cpus or maxcpus must be provided.
     Threads will default to 1 if not provided. Sockets and cores must be
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 307944aef3..69a5c73ef7 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -719,6 +719,9 @@ static QemuOptsList qemu_smp_opts = {
         }, {
             .name = "dies",
             .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "clusters",
+            .type = QEMU_OPT_NUMBER,
         }, {
             .name = "cores",
             .type = QEMU_OPT_NUMBER,
-- 
2.19.1