[Qemu-devel] [PULL 1/7] trace: Allocate cpu->trace_dstate in place

[Stefan Hajnoczi <stefanha@redhat.com>]

From: Lluís Vilanova <vilanova@ac.upc.edu>

There's little point in dynamically allocating the bitmap if we
know at compile-time the max number of events we want to support.
Thus, make room in the struct for the bitmap, which will make things
easier later: this paves the way for upcoming changes, in which
we'll use a u32 to fully capture cpu->trace_dstate.

This change also increases performance by saving a dereference and
improving locality--note that this is important since upcoming work
makes reading this bitmap fairly common.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Reviewed-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Message-id: 149915725977.6295.15069969323605305641.stgit@frigg.lan
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/qom/cpu.h | 9 +++------
 qom/cpu.c         | 8 --------
 trace/control.c   | 9 ++++++++-
 3 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 04c31e6..5f188d4 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -259,6 +259,7 @@ typedef void (*run_on_cpu_func)(CPUState *cpu, run_on_cpu_data data);
 struct qemu_work_item;
 
 #define CPU_UNSET_NUMA_NODE_ID -1
+#define CPU_TRACE_DSTATE_MAX_EVENTS 32
 
 /**
  * CPUState:
@@ -370,12 +371,8 @@ struct CPUState {
     struct KVMState *kvm_state;
     struct kvm_run *kvm_run;
 
-    /*
-     * Used for events with 'vcpu' and *without* the 'disabled' properties.
-     * Dynamically allocated based on bitmap requried to hold up to
-     * trace_get_vcpu_event_count() entries.
-     */
-    unsigned long *trace_dstate;
+    /* Used for events with 'vcpu' and *without* the 'disabled' properties */
+    DECLARE_BITMAP(trace_dstate, CPU_TRACE_DSTATE_MAX_EVENTS);
 
     /* TODO Move common fields from CPUArchState here. */
     int cpu_index; /* used by alpha TCG */
diff --git a/qom/cpu.c b/qom/cpu.c
index a39ff6c..4f38db0 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -380,7 +380,6 @@ static void cpu_common_unrealizefn(DeviceState *dev, Error **errp)
 
 static void cpu_common_initfn(Object *obj)
 {
-    uint32_t count;
     CPUState *cpu = CPU(obj);
     CPUClass *cc = CPU_GET_CLASS(obj);
 
@@ -395,18 +394,11 @@ static void cpu_common_initfn(Object *obj)
     QTAILQ_INIT(&cpu->breakpoints);
     QTAILQ_INIT(&cpu->watchpoints);
 
-    count = trace_get_vcpu_event_count();
-    if (count) {
-        cpu->trace_dstate = bitmap_new(count);
-    }
-
     cpu_exec_initfn(cpu);
 }
 
 static void cpu_common_finalize(Object *obj)
 {
-    CPUState *cpu = CPU(obj);
-    g_free(cpu->trace_dstate);
 }
 
 static int64_t cpu_common_get_arch_id(CPUState *cpu)
diff --git a/trace/control.c b/trace/control.c
index f5fb11d..82d8989 100644
--- a/trace/control.c
+++ b/trace/control.c
@@ -65,8 +65,15 @@ void trace_event_register_group(TraceEvent **events)
     size_t i;
     for (i = 0; events[i] != NULL; i++) {
         events[i]->id = next_id++;
-        if (events[i]->vcpu_id != TRACE_VCPU_EVENT_NONE) {
+        if (events[i]->vcpu_id == TRACE_VCPU_EVENT_NONE) {
+            continue;
+        }
+
+        if (likely(next_vcpu_id < CPU_TRACE_DSTATE_MAX_EVENTS)) {
             events[i]->vcpu_id = next_vcpu_id++;
+        } else {
+            error_report("WARNING: too many vcpu trace events; dropping '%s'",
+                         events[i]->name);
         }
     }
     event_groups = g_renew(TraceEventGroup, event_groups, nevent_groups + 1);
-- 
2.9.4