Re: [Qemu-devel] [PATCH v8 2/7] cpu: allocate cpu->trace_dstate in place

["Lluís Vilanova" <vilanova@ac.upc.edu>]

Lluís Vilanova writes:

> Emilio G Cota writes:
>> 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>

BTW, I think this partially undoes Daniel's changes in
b7d48952c375842bd669460fd8384d90cc12286c.

You should check with him (CC'ed).

Lluis


>> ---
>> 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 89ddb68..bc6e20f 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:
>> @@ -373,12 +374,8 @@ 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 5069876..69fbb9c 100644
>> --- a/qom/cpu.c
>> +++ b/qom/cpu.c
>> @@ -382,7 +382,6 @@ 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);
 
>> @@ -397,18 +396,11 @@ 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 9b157b0..83740aa 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);
>> -- 
>> 2.7.4