Re: [PATCH v5 1/9] target/arm/monitor: Introduce qmp_query_cpu_model_expansion

[Beata Michalska]

On Wed, 16 Oct 2019 at 14:50, Andrew Jones <address@hidden> wrote:
>
> On Wed, Oct 16, 2019 at 02:24:50PM +0100, Beata Michalska wrote:
> > On Tue, 15 Oct 2019 at 12:56, Beata Michalska
> > <address@hidden> wrote:
> > >
> > > On Tue, 15 Oct 2019 at 11:56, Andrew Jones <address@hidden> wrote:
> > > >
> > > > On Tue, Oct 15, 2019 at 10:59:16AM +0100, Beata Michalska wrote:
> > > > > On Tue, 1 Oct 2019 at 14:04, Andrew Jones <address@hidden> wrote:
> > > > > > +
> > > > > > +    obj = object_new(object_class_get_name(oc));
> > > > > > +
> > > > > > +    if (qdict_in) {
> > > > > > +        Visitor *visitor;
> > > > > > +        Error *err = NULL;
> > > > > > +
> > > > > > +        visitor = qobject_input_visitor_new(model->props);
> > > > > > +        visit_start_struct(visitor, NULL, NULL, 0, &err);
> > > > > > +        if (err) {
> > > > > > +            object_unref(obj);
> > > > >
> > > > > Shouldn't we free the 'visitor' here as well ?
> > > >
> > > > Yes. Good catch. So we also need to fix
> > > > target/s390x/cpu_models.c:cpu_model_from_info(), which has the same
> > > > construction (the construction from which I derived this)
> > > >
> > > > >
> > > > > > +            error_propagate(errp, err);
> > > > > > +            return NULL;
> > > > > > +        }
> > > > > > +
> > > >
> > > > What about the rest of the patch? With that fixed for v6 can I
> > > > add your r-b?
> > > >
> > >
> > > I still got this feeling that we could optimize that a bit - which I'm
> > > currently on, so hopefully I'll be able to add more comments soon if
> > > that proves to be the case.
> > >
> > > BR
> > > Beata
> >
> > I think there are few options that might be considered though the gain
> > is not huge .. but it's always smth:
> >
> > > +CpuModelExpansionInfo 
> > > *qmp_query_cpu_model_expansion(CpuModelExpansionType type,
> > > +                                                     CpuModelInfo *model,
> > > +                                                     Error **errp)
> > > +{
> > > +    CpuModelExpansionInfo *expansion_info;
> > > +    const QDict *qdict_in = NULL;
> > > +    QDict *qdict_out;
> > > +    ObjectClass *oc;
> > > +    Object *obj;
> > > +    const char *name;
> > > +    int i;
> > > +
> > > +    if (type != CPU_MODEL_EXPANSION_TYPE_FULL) {
> > > +        error_setg(errp, "The requested expansion type is not 
> > > supported");
> > > +        return NULL;
> > > +    }
> > > +
> > > +    if (!kvm_enabled() && !strcmp(model->name, "host")) {
> > > +        error_setg(errp, "The CPU type '%s' requires KVM", model->name);
> > > +        return NULL;
> > > +    }
> > > +
> > > +    oc = cpu_class_by_name(TYPE_ARM_CPU, model->name);
> > > +    if (!oc) {
> > > +        error_setg(errp, "The CPU type '%s' is not a recognized ARM CPU 
> > > type",
> > > +                   model->name);
> > > +        return NULL;
> > > +    }
> > > +
> > > +    if (kvm_enabled()) {
> > > +        const char *cpu_type = current_machine->cpu_type;
> > > +        int len = strlen(cpu_type) - strlen(ARM_CPU_TYPE_SUFFIX);
> > > +        bool supported = false;
> > > +
> > > +        if (!strcmp(model->name, "host") || !strcmp(model->name, "max")) 
> > > {
> > > +            /* These are kvmarm's recommended cpu types */
> > > +            supported = true;
> > > +        } else if (strlen(model->name) == len &&
> > > +                   !strncmp(model->name, cpu_type, len)) {
> > > +            /* KVM is enabled and we're using this type, so it works. */
> > > +            supported = true;
> > > +        }
> > > +        if (!supported) {
> > > +            error_setg(errp, "We cannot guarantee the CPU type '%s' 
> > > works "
> > > +                             "with KVM on this host", model->name);
> > > +            return NULL;
> > > +        }
> > > +    }
> > > +
> >
> > The above section can be slightly reduced and rearranged - preferably
> > moved to a separate function
> > -> get_cpu_model (...) ?
> >
> > * You can check the 'host' model first and then validate the accelerator ->
> >     if ( !strcmp(model->name, "host")
> >         if (!kvm_enabled())
> >             log_error & leave
> >        else
> >           goto cpu_class_by_name /*cpu_class_by_name moved after the
> > final model check @see below */
> >
> > * the kvm_enabled section can be than slightly improved (dropping the
> > second compare against 'host')
> >
> >       if (kvm_enabled() && strcmp(model->name, "max") {
> >            /*Validate the current_machine->cpu_type against the
> > model->name and report error case mismatch
> >           /* otherwise just fall through */
> >       }
> >  * cpu_class_by_name moved here ...
> > > +    if (model->props) {
> > MInor: the CPUModelInfo seems to have dedicated field for that
> > verification -> has_props
> >
> > > +        qdict_in = qobject_to(QDict, model->props);
> > > +        if (!qdict_in) {
> > > +            error_setg(errp, QERR_INVALID_PARAMETER_TYPE, "props", 
> > > "dict");
> > > +            return NULL;
> > > +        }
> > > +    }
> > > +
> > > +    obj = object_new(object_class_get_name(oc));
> > > +
> > > +    if (qdict_in) {
> > > +        Visitor *visitor;
> > > +        Error *err = NULL;
> > > +
> > > +        visitor = qobject_input_visitor_new(model->props);
> > > +        visit_start_struct(visitor, NULL, NULL, 0, &err);
> > > +        if (err) {
> > > +            object_unref(obj);
> > > +            error_propagate(errp, err);
> > > +            return NULL;
> > > +        }
> > > +
> > > +        i = 0;
> > > +        while ((name = cpu_model_advertised_features[i++]) != NULL) {
> > > +            if (qdict_get(qdict_in, name)) {
> > > +                object_property_set(obj, visitor, name, &err);
> > > +                if (err) {
> > > +                    break;
> > > +                }
> > > +            }
> > > +        }
> > > +
> > > +        if (!err) {
> > > +            visit_check_struct(visitor, &err);
> > > +        }
> > > +        visit_end_struct(visitor, NULL);
> > > +        visit_free(visitor);
> > > +        if (err) {
> > > +            object_unref(obj);
> > > +            error_propagate(errp, err);
> > > +            return NULL;
> > > +        }
> > > +    }
> >
> > The both >> if (err) << blocks could be extracted and moved at the end
> > of the function
> > to mark a 'cleanup section'  and both here and few lines before
> > (with the visit_start_struct failure) could use goto.
> > Easier to maintain and to make sure we make the proper cleanup in any case.
> >
> > > +
> > > +    expansion_info = g_new0(CpuModelExpansionInfo, 1);
> > > +    expansion_info->model = g_malloc0(sizeof(*expansion_info->model));
> > > +    expansion_info->model->name = g_strdup(model->name);
> > > +
> > > +    qdict_out = qdict_new();
> > > +
> > > +    i = 0;
> > > +    while ((name = cpu_model_advertised_features[i++]) != NULL) {
> > > +        ObjectProperty *prop = object_property_find(obj, name, NULL);
> > > +        if (prop) {
> > > +            Error *err = NULL;
> > > +            QObject *value;
> > > +
> > > +            assert(prop->get);
> > > +            value = object_property_get_qobject(obj, name, &err);
> > > +            assert(!err);
> > > +
> > > +            qdict_put_obj(qdict_out, name, value);
> > > +        }
> > > +    }
> > > +
> >
> > This could be merged with the first iteration over the features,
> > smth like:
> >
> >     while () {
> >         if ((value = qdict_get(qdict_in, name))) {
> >             object_property_set ...
> >            if (!err)
> >                qobject_ref(value) /* we have the weak reference */
> >             else
> >                 break;
> >         } else {
> >              value = object_property_get_qobject()
> >         }
> >         if (value) qdict_put_object(qdict_out, name, value)
> >     }
> >
> > This way you iterate over the table once and you do not query
> > for the same property twice by getting the value from the qdict_in.
> > If the value is not acceptable we will fail either way so should be all 
> > good.
> >
> >
> > > +    if (!qdict_size(qdict_out)) {
> > > +        qobject_unref(qdict_out);
> > > +    } else {
> > > +        expansion_info->model->props = QOBJECT(qdict_out);
> > > +        expansion_info->model->has_props = true;
> > > +    }
> > > +
> > > +    object_unref(obj);
> > > +
> > > +    return expansion_info;
> >
> > Mentioned earlier cleanup section:
> > cleanup:
> >    object_unref(obj);
> >    qobject_unref(qdict_out) ; /* if single loop is used */
> >    error_propagate(errp,err);
> >    return NULL;
> >
> > > +}
> > > --
> > > 2.20.1
> > >
> >
> > Hope I haven't missed anything.
> > What do you think ?
> >
>
> I think you need to post an entire function that incorporates all the
> proposed changes, or at least a diff that I can apply in order to get
> the entirely changed function. I also think that it's fine the way
> it is, so it would take a justification stronger than a potential
> micro optimization to get me to change it.
>

The numbers I can pull out of it are not thrilling and this is not
on a fast path so I will not be pushing for changes.
Though extracting the clean-up might be worth considering -
for improved maintenance.

For a reference though:

_______________________________________________________

---
 target/arm/monitor.c | 100 +++++++++++++++++++++++++--------------------------
 1 file changed, 50 insertions(+), 50 deletions(-)

diff --git a/target/arm/monitor.c b/target/arm/monitor.c
index edca8aa..0d6bd42 100644
--- a/target/arm/monitor.c
+++ b/target/arm/monitor.c
@@ -112,17 +112,40 @@ CpuModelExpansionInfo
*qmp_query_cpu_model_expansion(CpuModelExpansionType type,
     Object *obj;
     const char *name;
     int i;
+    Error *err = NULL;

     if (type != CPU_MODEL_EXPANSION_TYPE_FULL) {
         error_setg(errp, "The requested expansion type is not supported");
         return NULL;
     }

-    if (!kvm_enabled() && !strcmp(model->name, "host")) {
-        error_setg(errp, "The CPU type '%s' requires KVM", model->name);
-        return NULL;
+    /* CPU type => 'host' */
+    if (!strcmp(model->name, "host")) {
+        if (!kvm_enabled()) {
+            error_setg(errp, "The CPU type '%s' requires KVM", model->name);
+            return NULL;
+        } else {
+            goto valid;
+        }
+    }
+
+
+    /* Case when KVM is enabled and the model is a specific cpu model ... */
+    if (kvm_enabled() && strcmp(model->name, "max")) {
+            const char *cpu_type = current_machine->cpu_type;
+            int len = strlen(cpu_type) - strlen("-" TYPE_ARM_CPU);
+
+            if (strlen(model->name) == len
+             && !strncmp(cpu_type, model->name, len)) {
+                error_setg(errp, "We cannot guarantee the CPU type '%s' works "
+                        "with KVM on this host", model->name);
+                return NULL;
+            }
+
     }

+valid:
+
     oc = cpu_class_by_name(TYPE_ARM_CPU, model->name);
     if (!oc) {
         error_setg(errp, "The CPU type '%s' is not a recognized ARM CPU type",
@@ -130,25 +153,6 @@ CpuModelExpansionInfo
*qmp_query_cpu_model_expansion(CpuModelExpansionType type,
         return NULL;
     }

-    if (kvm_enabled()) {
-        const char *cpu_type = current_machine->cpu_type;
-        int len = strlen(cpu_type) - strlen(ARM_CPU_TYPE_SUFFIX);
-        bool supported = false;
-
-        if (!strcmp(model->name, "host") || !strcmp(model->name, "max")) {
-            /* These are kvmarm's recommended cpu types */
-            supported = true;
-        } else if (strlen(model->name) == len &&
-                   !strncmp(model->name, cpu_type, len)) {
-            /* KVM is enabled and we're using this type, so it works. */
-            supported = true;
-        }
-        if (!supported) {
-            error_setg(errp, "We cannot guarantee the CPU type '%s' works "
-                             "with KVM on this host", model->name);
-            return NULL;
-        }
-    }

     if (model->props) {
         qdict_in = qobject_to(QDict, model->props);
@@ -159,62 +163,52 @@ CpuModelExpansionInfo
*qmp_query_cpu_model_expansion(CpuModelExpansionType type,
     }

     obj = object_new(object_class_get_name(oc));
+    qdict_out = qdict_new();

     if (qdict_in) {
         Visitor *visitor;
-        Error *err = NULL;
+        QObject *value;

         visitor = qobject_input_visitor_new(model->props);
         visit_start_struct(visitor, NULL, NULL, 0, &err);
         if (err) {
-            object_unref(obj);
-            error_propagate(errp, err);
-            return NULL;
+            visit_free(visitor);
+            goto cleanup;
         }
-
         i = 0;
         while ((name = cpu_model_advertised_features[i++]) != NULL) {
-            if (qdict_get(qdict_in, name)) {
+            value = qdict_get(qdict_in, name);
+            if (value) {
                 object_property_set(obj, visitor, name, &err);
-                if (err) {
+                if (!err) {
+                    qobject_ref(value);
+                } else {
                     break;
                 }
+
+            } else {
+               value = object_property_get_qobject(obj, name, &err);
             }
-        }

+            if (value) {
+                qdict_put_obj(qdict_out, name, value);
+            }
+        }
         if (!err) {
             visit_check_struct(visitor, &err);
         }
         visit_end_struct(visitor, NULL);
         visit_free(visitor);
         if (err) {
-            object_unref(obj);
-            error_propagate(errp, err);
-            return NULL;
+            goto cleanup;
         }
+
     }

     expansion_info = g_new0(CpuModelExpansionInfo, 1);
     expansion_info->model = g_malloc0(sizeof(*expansion_info->model));
     expansion_info->model->name = g_strdup(model->name);

-    qdict_out = qdict_new();
-
-    i = 0;
-    while ((name = cpu_model_advertised_features[i++]) != NULL) {
-        ObjectProperty *prop = object_property_find(obj, name, NULL);
-        if (prop) {
-            Error *err = NULL;
-            QObject *value;
-
-            assert(prop->get);
-            value = object_property_get_qobject(obj, name, &err);
-            assert(!err);
-
-            qdict_put_obj(qdict_out, name, value);
-        }
-    }
-
     if (!qdict_size(qdict_out)) {
         qobject_unref(qdict_out);
     } else {
@@ -225,4 +219,10 @@ CpuModelExpansionInfo
*qmp_query_cpu_model_expansion(CpuModelExpansionType type,
     object_unref(obj);

     return expansion_info;
+
+cleanup:
+    object_unref(obj);
+    qobject_unref(qdict_out);
+    error_propagate(errp, err);
+    return NULL;
 }
-- 
2.7.4

BR
Beata

> Thanks,
> drew