Re: [PATCH 10/18] ppc: Add has_smt_siblings property to CPUPPCState

[Cédric Le Goater]

On 7/11/24 16:18, Nicholas Piggin wrote:

The decision to branch out to a slower SMT path in instruction
emulation will become a bit more complicated with the way that
"big-core" topology that will be implemented in subsequent changes.
Hide these details from the wider CPU emulation code with a bool
has_smt_siblings flag that can be set by machine initialisation.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>

The distinction between what's done in pnv_core_realize() and
pnv_core_cpu_realize() is not clear. Not this patch fault though.

Reviewed-by: Cédric Le Goater <c...@redhat.com>

Thanks,

C.

---
  target/ppc/cpu.h        |  3 ++-
  hw/ppc/pnv_core.c       |  3 +++
  hw/ppc/spapr_cpu_core.c | 15 +++++++++++----
  3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index a74b753c99..35a1cb65cb 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -1248,6 +1248,7 @@ struct CPUArchState {
      int access_type;

/* For SMT processors */

+    bool has_smt_siblings;
      int core_index;

#if !defined(CONFIG_USER_ONLY)

@@ -1516,7 +1517,7 @@ struct PowerPCCPUClass {

static inline bool ppc_cpu_core_single_threaded(CPUState *cs)

  {
-    return cs->nr_threads == 1;
+    return !POWERPC_CPU(cs)->env.has_smt_siblings;
  }

static inline bool ppc_cpu_lpar_single_threaded(CPUState *cs)

diff --git a/hw/ppc/pnv_core.c b/hw/ppc/pnv_core.c
index 7bda29b9c7..8cfa94fbfa 100644
--- a/hw/ppc/pnv_core.c
+++ b/hw/ppc/pnv_core.c
@@ -288,6 +288,9 @@ static void pnv_core_realize(DeviceState *dev, Error **errp)
          cpu = POWERPC_CPU(obj);

pc->threads[i] = POWERPC_CPU(obj);

+        if (cc->nr_threads > 1) {
+            cpu->env.has_smt_siblings = true;
+        }

snprintf(name, sizeof(name), "thread[%d]", i);

          object_property_add_child(OBJECT(pc), name, obj);
diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
index d9116c8409..2c6eeb41a4 100644
--- a/hw/ppc/spapr_cpu_core.c
+++ b/hw/ppc/spapr_cpu_core.c
@@ -314,12 +314,13 @@ static PowerPCCPU *spapr_create_vcpu(SpaprCpuCore *sc, 
int i, Error **errp)
       * and the rest are explicitly started up by the guest using an RTAS call.
       */
      qdev_prop_set_bit(DEVICE(obj), "start-powered-off", true);
-    env->core_index = cc->core_id;
      cs->cpu_index = cc->core_id + i;
      if (!spapr_set_vcpu_id(cpu, cs->cpu_index, errp)) {
          return NULL;
      }

+ env->core_index = cc->core_id;

+
      cpu->node_id = sc->node_id;

id = g_strdup_printf("thread[%d]", i);

@@ -350,9 +351,15 @@ static void spapr_cpu_core_realize(DeviceState *dev, Error 
**errp)
      qemu_register_reset(spapr_cpu_core_reset_handler, sc);
      sc->threads = g_new0(PowerPCCPU *, cc->nr_threads);
      for (i = 0; i < cc->nr_threads; i++) {
-        sc->threads[i] = spapr_create_vcpu(sc, i, errp);
-        if (!sc->threads[i] ||
-            !spapr_realize_vcpu(sc->threads[i], spapr, sc, i, errp)) {
+        PowerPCCPU *cpu;
+
+        cpu = spapr_create_vcpu(sc, i, errp);
+        sc->threads[i] = cpu;
+        if (cpu && cc->nr_threads > 1) {
+            cpu->env.has_smt_siblings = true;
+        }
+
+        if (!cpu || !spapr_realize_vcpu(cpu, spapr, sc, i, errp)) {
              spapr_cpu_core_unrealize(dev);
              return;
          }