On Sun, Jun 25, 2017 at 12:41:57PM +0300, Lluís Vilanova wrote:
> 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 <c...@braap.org>
>
> > Reviewed-by: Lluís Vilanova <vilan...@ac.upc.edu>
>
> BTW, I think this partially undoes Daniel's changes in
> b7d48952c375842bd669460fd8384d90cc12286c.
>
> You should check with him (CC'ed).
That's ok - I only made those changes in order to remove the reliance on
the generated max vcpu event ID counter. Choosing to hardcode a fixed
limit on number of vcpu events instead is a fine alternative.
>
> 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);
> >> }
This should be an abort IMHO, as it would be considered a bug to have
added > 32 vcpu events.
I'd also suggest that the top level 'trace-events' file get a comment
added to the effect that we only support 32 events right now.
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
