[RFC PATCH 3/6] hw/arm/virt: Parse cluster cpu topology for ARM machines

[Yanan Wang]

There is a separate function virt_smp_parse() in hw/virt/arm.c used
to parse cpu topology for the ARM machines. And there are some ARM
implementations that have the concept of cluster, for example, ARM64
server chip Kunpeng 920 has 6 or 8 clusters in each NUMA node and each
cluster has 4 cores. All clusters share L3 cache data while the cores
within each cluster share L2 cache. So parse cluster cpu topology for
ARM machines, then guest kernel will take advantages of it for better
scheduling performance.

In virt_smp_parse(), the computing logic of missing values prefers
cores over sockets over threads. And the value of clusters will be
set as default 1 if not explictly specified, so that it will not
impact the parsing results of machines that won't specify "clusters="
in -smp command line because they just don't support it.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
 hw/arm/virt.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 911ad7d3aa..c9ad76ff64 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2608,35 +2608,37 @@ static void virt_smp_parse(MachineState *ms, QemuOpts 
*opts)
     if (opts) {
         unsigned cpus    = qemu_opt_get_number(opts, "cpus", 0);
         unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
+        unsigned clusters = qemu_opt_get_number(opts, "clusters", 1);
         unsigned cores   = qemu_opt_get_number(opts, "cores", 0);
         unsigned threads = qemu_opt_get_number(opts, "threads", 0);
 
         /*
-         * Compute missing values; prefer cores over sockets and
-         * sockets over threads.
+         * Compute missing values, prefer cores over sockets
+         * and sockets over threads. The value of clusters has
+         * been be set as default 1 if not explicitly specified.
          */
         if (cpus == 0 || cores == 0) {
             sockets = sockets > 0 ? sockets : 1;
             threads = threads > 0 ? threads : 1;
             if (cpus == 0) {
                 cores = cores > 0 ? cores : 1;
-                cpus = cores * threads * sockets;
+                cpus = sockets * clusters * cores * threads;
             } else {
                 ms->smp.max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
-                cores = ms->smp.max_cpus / (sockets * threads);
+                cores = ms->smp.max_cpus / (sockets * clusters * threads);
             }
         } else if (sockets == 0) {
             threads = threads > 0 ? threads : 1;
-            sockets = cpus / (cores * threads);
+            sockets = cpus / (clusters * cores * threads);
             sockets = sockets > 0 ? sockets : 1;
         } else if (threads == 0) {
-            threads = cpus / (cores * sockets);
+            threads = cpus / (sockets * clusters * cores);
             threads = threads > 0 ? threads : 1;
-        } else if (sockets * cores * threads < cpus) {
+        } else if (sockets * clusters * cores * threads < cpus) {
             error_report("cpu topology: "
-                         "sockets (%u) * cores (%u) * threads (%u) < "
-                         "smp_cpus (%u)",
-                         sockets, cores, threads, cpus);
+                         "sockets (%u) * clusters (%u) * cores (%u) * "
+                         "threads (%u) < smp_cpus (%u)",
+                         sockets, clusters, cores, threads, cpus);
             exit(1);
         }
 
@@ -2647,16 +2649,17 @@ static void virt_smp_parse(MachineState *ms, QemuOpts 
*opts)
             exit(1);
         }
 
-        if (sockets * cores * threads != ms->smp.max_cpus) {
+        if (sockets * clusters * cores * threads != ms->smp.max_cpus) {
             error_report("cpu topology: "
-                         "sockets (%u) * cores (%u) * threads (%u)"
-                         "!= maxcpus (%u)",
-                         sockets, cores, threads,
+                         "sockets (%u) * clusters(%u) * cores (%u) * "
+                         "threads (%u) != maxcpus (%u)",
+                         sockets, clusters, cores, threads,
                          ms->smp.max_cpus);
             exit(1);
         }
 
         ms->smp.cpus = cpus;
+        ms->smp.clusters = clusters;
         ms->smp.cores = cores;
         ms->smp.threads = threads;
         ms->smp.sockets = sockets;
-- 
2.19.1