[RFC PATCH v2 6/6] hw/arm/virt: Replace smp_parse with one that prefers cores

[Yanan Wang]

From: Andrew Jones <drjones@redhat.com>

The virt machine type has never used the CPU topology parameters, other
than number of online CPUs and max CPUs. When choosing how to allocate
those CPUs the default has been to assume cores. In preparation for
using the other CPU topology parameters let's use an smp_parse that
prefers cores over sockets. We can also enforce the topology matches
max_cpus check because we have no legacy to preserve.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
---
 hw/arm/virt.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 3e5d9b6f26..57ef961cb5 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -79,6 +79,8 @@
 #include "hw/virtio/virtio-iommu.h"
 #include "hw/char/pl011.h"
 #include "qemu/guest-random.h"
+#include "qapi/qmp/qerror.h"
+#include "sysemu/replay.h"
 
 #define DEFINE_VIRT_MACHINE_LATEST(major, minor, latest) \
     static void virt_##major##_##minor##_class_init(ObjectClass *oc, \
@@ -2625,6 +2627,79 @@ static int virt_kvm_type(MachineState *ms, const char 
*type_str)
     return fixed_ipa ? 0 : requested_pa_size;
 }
 
+/*
+ * Unlike smp_parse() in hw/core/machine.c, we prefer cores over sockets,
+ * e.g. '-smp 8' creates 1 socket with 8 cores.  Whereas '-smp 8' with
+ * hw/core/machine.c's smp_parse() creates 8 sockets, each with 1 core.
+ * Additionally, we can enforce the topology matches max_cpus check,
+ * because we have no legacy to preserve.
+ */
+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 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.
+         */
+        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;
+            } else {
+                ms->smp.max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
+                cores = ms->smp.max_cpus / (sockets * threads);
+            }
+        } else if (sockets == 0) {
+            threads = threads > 0 ? threads : 1;
+            sockets = cpus / (cores * threads);
+            sockets = sockets > 0 ? sockets : 1;
+        } else if (threads == 0) {
+            threads = cpus / (cores * sockets);
+            threads = threads > 0 ? threads : 1;
+        } else if (sockets * cores * threads < cpus) {
+            error_report("cpu topology: "
+                         "sockets (%u) * cores (%u) * threads (%u) < "
+                         "smp_cpus (%u)",
+                         sockets, cores, threads, cpus);
+            exit(1);
+        }
+
+        ms->smp.max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
+
+        if (ms->smp.max_cpus < cpus) {
+            error_report("maxcpus must be equal to or greater than smp");
+            exit(1);
+        }
+
+        if (sockets * cores * threads != ms->smp.max_cpus) {
+            error_report("cpu topology: "
+                         "sockets (%u) * cores (%u) * threads (%u)"
+                         "!= maxcpus (%u)",
+                         sockets, cores, threads,
+                         ms->smp.max_cpus);
+            exit(1);
+        }
+
+        ms->smp.cpus = cpus;
+        ms->smp.cores = cores;
+        ms->smp.threads = threads;
+        ms->smp.sockets = sockets;
+    }
+
+    if (ms->smp.cpus > 1) {
+        Error *blocker = NULL;
+        error_setg(&blocker, QERR_REPLAY_NOT_SUPPORTED, "smp");
+        replay_add_blocker(blocker);
+    }
+}
+
 static void virt_machine_class_init(ObjectClass *oc, void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
@@ -2650,6 +2725,7 @@ static void virt_machine_class_init(ObjectClass *oc, void 
*data)
     mc->cpu_index_to_instance_props = virt_cpu_index_to_props;
     mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a15");
     mc->get_default_cpu_node_id = virt_get_default_cpu_node_id;
+    mc->smp_parse = virt_smp_parse;
     mc->kvm_type = virt_kvm_type;
     assert(!mc->get_hotplug_handler);
     mc->get_hotplug_handler = virt_machine_get_hotplug_handler;
-- 
2.19.1