[sysprof/wip/visualizers] cpu: discover cpu counters from SpCaptureReader

[Christian Hergert <chergert src gnome org>]

commit 3b9ea07d31c12d37e8ad72ed62fe7116febfeaf8
Author: Christian Hergert <chergert redhat com>
Date:   Sun Sep 25 12:19:53 2016 -0700

    cpu: discover cpu counters from SpCaptureReader
    
    This allows us to dynamically discover the cpu counters from the
    capture by looking for the "CPU Total" category.

 lib/Makefile.am               |    2 +
 lib/sp-cpu-visualizer-row.c   |  156 ++++++++++++++++++++++++++++++++
 lib/sp-cpu-visualizer-row.h   |   34 +++++++
 lib/sp-line-visualizer-row.c  |  198 +++++++++++++++++++++++-----------------
 lib/sp-line-visualizer-row.h  |   31 ++++++-
 src/resources/ui/sp-window.ui |    2 +-
 6 files changed, 337 insertions(+), 86 deletions(-)
---
diff --git a/lib/Makefile.am b/lib/Makefile.am
index b31ff98..42da2ab 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -137,6 +137,7 @@ uiheadersdir = $(includedir)/sysprof-@API_VERSION@
 uiheaders_DATA = \
        sp-callgraph-view.h \
        sp-cell-renderer-percent.h \
+       sp-cpu-visualizer-row.h \
        sp-empty-state-view.h \
        sp-failed-state-view.h \
        sp-line-visualizer-row.h \
@@ -154,6 +155,7 @@ libsysprof_ui_@API_VERSION@_la_SOURCES = \
        $(uiheaders_DATA) \
        sp-callgraph-view.c \
        sp-cell-renderer-percent.c \
+       sp-cpu-visualizer-row.c \
        sp-empty-state-view.c \
        sp-failed-state-view.c \
        sp-line-visualizer-row.c \
diff --git a/lib/sp-cpu-visualizer-row.c b/lib/sp-cpu-visualizer-row.c
new file mode 100644
index 0000000..cc2bc4b
--- /dev/null
+++ b/lib/sp-cpu-visualizer-row.c
@@ -0,0 +1,156 @@
+/* sp-cpu-visualizer-row.c
+ *
+ * Copyright (C) 2016 Christian Hergert <chergert redhat com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define G_LOG_DOMAIN "sp-cpu-visualizer-row"
+
+#include "sp-capture-condition.h"
+#include "sp-capture-cursor.h"
+#include "sp-cpu-visualizer-row.h"
+
+struct _SpCpuVisualizerRow
+{
+  SpLineVisualizerRow parent_instance;
+};
+
+G_DEFINE_TYPE (SpCpuVisualizerRow, sp_cpu_visualizer_row, SP_TYPE_LINE_VISUALIZER_ROW)
+
+static gboolean
+sp_cpu_visualizer_counter_found (const SpCaptureFrame *frame,
+                                 gpointer              user_data)
+{
+  const SpCaptureFrameCounterDefine *def = (SpCaptureFrameCounterDefine *)frame;
+  GArray *counters = user_data;
+
+  g_assert (frame->type == SP_CAPTURE_FRAME_CTRDEF);
+
+  for (guint i = 0; i < def->n_counters; i++)
+    {
+      if (g_str_equal (def->counters[i].category, "CPU Percent"))
+        {
+          guint id = def->counters[i].id;
+          g_array_append_val (counters, id);
+        }
+    }
+
+  return TRUE;
+}
+
+static void
+sp_cpu_visualizer_row_discover_counters (GTask        *task,
+                                         gpointer      source_object,
+                                         gpointer      task_data,
+                                         GCancellable *canellable)
+{
+  const SpCaptureFrameType types[] = { SP_CAPTURE_FRAME_CTRDEF };
+  SpCaptureReader *reader = task_data;
+  g_autoptr(SpCaptureCursor) cursor = NULL;
+  SpCpuVisualizerRow *self = source_object;
+  g_autoptr(GArray) counters = NULL;
+
+  g_assert (G_IS_TASK (task));
+  g_assert (SP_IS_CPU_VISUALIZER_ROW (self));
+  g_assert (reader != NULL);
+
+  counters = g_array_new (FALSE, FALSE, sizeof (guint));
+  cursor = sp_capture_cursor_new (reader);
+  sp_capture_cursor_add_condition (cursor, sp_capture_condition_new_where_type_in (G_N_ELEMENTS (types), 
types));
+  sp_capture_cursor_foreach (cursor, sp_cpu_visualizer_counter_found, counters);
+  g_task_return_pointer (task, g_steal_pointer (&counters), (GDestroyNotify)g_array_unref);
+}
+
+static void
+complete_counters (GObject      *object,
+                   GAsyncResult *result,
+                   gpointer      user_data)
+{
+  SpCpuVisualizerRow *self = (SpCpuVisualizerRow *)object;
+  g_autoptr(GArray) counters = NULL;
+
+  g_assert (SP_IS_CPU_VISUALIZER_ROW (self));
+  g_assert (G_IS_TASK (result));
+
+  counters = g_task_propagate_pointer (G_TASK (result), NULL);
+
+  if (counters != NULL)
+    {
+      for (guint i = 0; i < counters->len; i++)
+        {
+          guint counter_id = g_array_index (counters, guint, i);
+
+          sp_line_visualizer_row_add_counter (SP_LINE_VISUALIZER_ROW (self), counter_id);
+        }
+    }
+}
+
+static void
+sp_cpu_visualizer_row_set_reader (SpVisualizerRow *row,
+                                  SpCaptureReader *reader)
+{
+  SpCpuVisualizerRow *self = (SpCpuVisualizerRow *)row;
+  g_autoptr(GTask) task = NULL;
+
+  g_assert (SP_IS_CPU_VISUALIZER_ROW (row));
+
+  sp_line_visualizer_row_clear (SP_LINE_VISUALIZER_ROW (row));
+
+  SP_VISUALIZER_ROW_CLASS (sp_cpu_visualizer_row_parent_class)->set_reader (row, reader);
+
+  if (reader != NULL)
+    {
+      task = g_task_new (self, NULL, complete_counters, NULL);
+      g_task_set_source_tag (task, sp_cpu_visualizer_row_set_reader);
+      g_task_set_task_data (task, sp_capture_reader_copy (reader),
+                            (GDestroyNotify)sp_capture_reader_unref);
+      g_task_run_in_thread (task, sp_cpu_visualizer_row_discover_counters);
+    }
+}
+
+static void
+sp_cpu_visualizer_row_prepare (SpLineVisualizerRow *row,
+                               cairo_t             *cr,
+                               guint                counter_id)
+{
+  g_assert (SP_IS_LINE_VISUALIZER_ROW (row));
+  g_assert (cr != NULL);
+  g_assert (counter_id > 0);
+
+  cairo_set_source_rgba (cr, 0, 0, 0, 0.4);
+  cairo_set_line_width (cr, 1.0);
+}
+
+static void
+sp_cpu_visualizer_row_class_init (SpCpuVisualizerRowClass *klass)
+{
+  SpLineVisualizerRowClass *line_class = SP_LINE_VISUALIZER_ROW_CLASS (klass);
+  SpVisualizerRowClass *row_class = SP_VISUALIZER_ROW_CLASS (klass);
+
+  row_class->set_reader = sp_cpu_visualizer_row_set_reader;
+
+  line_class->prepare = sp_cpu_visualizer_row_prepare;
+}
+
+static void
+sp_cpu_visualizer_row_init (SpCpuVisualizerRow *self)
+{
+}
+
+GtkWidget *
+sp_cpu_visualizer_row_new (void)
+{
+  return g_object_new (SP_TYPE_CPU_VISUALIZER_ROW, NULL);
+}
diff --git a/lib/sp-cpu-visualizer-row.h b/lib/sp-cpu-visualizer-row.h
new file mode 100644
index 0000000..7683caa
--- /dev/null
+++ b/lib/sp-cpu-visualizer-row.h
@@ -0,0 +1,34 @@
+/* sp-cpu-visualizer-row.h
+ *
+ * Copyright (C) 2016 Christian Hergert <chergert redhat com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef SP_CPU_VISUALIZER_ROW_H
+#define SP_CPU_VISUALIZER_ROW_H
+
+#include "sp-line-visualizer-row.h"
+
+G_BEGIN_DECLS
+
+#define SP_TYPE_CPU_VISUALIZER_ROW (sp_cpu_visualizer_row_get_type())
+
+G_DECLARE_FINAL_TYPE (SpCpuVisualizerRow, sp_cpu_visualizer_row, SP, CPU_VISUALIZER_ROW, SpLineVisualizerRow)
+
+GtkWidget *sp_cpu_visualizer_row_new (void);
+
+G_END_DECLS
+
+#endif /* SP_CPU_VISUALIZER_ROW_H */
diff --git a/lib/sp-line-visualizer-row.c b/lib/sp-line-visualizer-row.c
index 0ae5826..d359472 100644
--- a/lib/sp-line-visualizer-row.c
+++ b/lib/sp-line-visualizer-row.c
@@ -16,6 +16,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#define G_LOG_DOMAIN "sp-line-visualizer-row"
+
 #include <stdlib.h>
 
 #include "sp-line-visualizer-row.h"
@@ -33,23 +35,20 @@ typedef struct
   GArray *values;
 } LineData;
 
-struct _SpLineVisualizerRow
+typedef struct
 {
-  SpVisualizerRow  parent_instance;
-
   SpCaptureReader *reader;
 
   GHashTable      *counters;
-
   GtkLabel        *label;
 
-  guint            needs_recalc : 1;
-
   gint64           start_time;
   gint64           duration;
-};
 
-G_DEFINE_TYPE (SpLineVisualizerRow, sp_line_visualizer_row, SP_TYPE_VISUALIZER_ROW)
+  guint            needs_recalc : 1;
+} SpLineVisualizerRowPrivate;
+
+G_DEFINE_TYPE_WITH_PRIVATE (SpLineVisualizerRow, sp_line_visualizer_row, SP_TYPE_VISUALIZER_ROW)
 
 enum {
   PROP_0,
@@ -74,47 +73,56 @@ line_data_free (gpointer data)
 static void
 sp_line_visualizer_row_recalc (SpLineVisualizerRow *self)
 {
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
   GHashTable *new_data;
   SpCaptureFrame frame;
 
   g_assert (SP_IS_LINE_VISUALIZER_ROW (self));
 
-  self->needs_recalc = FALSE;
+  /*
+   * TODO:
+   *
+   * We want to create an index that gives us quick access to this
+   * data without quite so much overhead that we have now. The 16
+   * bytes per data-point is pretty high.
+   */
 
-  if (self->reader == NULL)
+  priv->needs_recalc = FALSE;
+
+  if (priv->reader == NULL)
     return;
 
-  sp_capture_reader_reset (self->reader);
+  sp_capture_reader_reset (priv->reader);
 
-  self->start_time = sp_capture_reader_get_start_time (self->reader);
-  self->duration = 0;
+  priv->start_time = sp_capture_reader_get_start_time (priv->reader);
+  priv->duration = 0;
 
   new_data = g_hash_table_new_full (NULL, NULL, NULL, line_data_free);
 
-  while (sp_capture_reader_peek_frame (self->reader, &frame))
+  while (sp_capture_reader_peek_frame (priv->reader, &frame))
     {
       gint64 relative;
 
-      if (frame.time < self->start_time)
-        frame.time = self->start_time;
+      if (frame.time < priv->start_time)
+        frame.time = priv->start_time;
 
-      relative = frame.time - self->start_time;
-      if (relative > self->duration)
-        self->duration = relative;
+      relative = frame.time - priv->start_time;
+      if (relative > priv->duration)
+        priv->duration = relative;
 
       if (frame.type == SP_CAPTURE_FRAME_CTRDEF)
         {
           const SpCaptureFrameCounterDefine *def;
           guint i;
 
-          if (NULL == (def = sp_capture_reader_read_counter_define (self->reader)))
+          if (NULL == (def = sp_capture_reader_read_counter_define (priv->reader)))
             return;
 
           for (i = 0; i < def->n_counters; i++)
             {
               const SpCaptureCounter *ctr = &def->counters[i];
 
-              if (g_hash_table_contains (self->counters, GSIZE_TO_POINTER (ctr->id)))
+              if (g_hash_table_contains (priv->counters, GSIZE_TO_POINTER (ctr->id)))
                 {
                   LineData *ld = g_hash_table_lookup (new_data, GSIZE_TO_POINTER (ctr->id));
                   LineDataItem item;
@@ -128,7 +136,7 @@ sp_line_visualizer_row_recalc (SpLineVisualizerRow *self)
                       g_hash_table_insert (new_data, GSIZE_TO_POINTER (ctr->id), ld);
                     }
 
-                  item.time = MAX (self->start_time, def->frame.time) - self->start_time;
+                  item.time = MAX (priv->start_time, def->frame.time) - priv->start_time;
                   item.value = ctr->value;
 
                   g_array_append_val (ld->values, item);
@@ -141,10 +149,10 @@ sp_line_visualizer_row_recalc (SpLineVisualizerRow *self)
           LineDataItem item;
           guint i;
 
-          if (NULL == (set = sp_capture_reader_read_counter_set (self->reader)))
+          if (NULL == (set = sp_capture_reader_read_counter_set (priv->reader)))
             return;
 
-          item.time = MAX (self->start_time, set->frame.time) - self->start_time;
+          item.time = MAX (priv->start_time, set->frame.time) - priv->start_time;
 
           for (i = 0; i < set->n_values; i++)
             {
@@ -170,20 +178,12 @@ sp_line_visualizer_row_recalc (SpLineVisualizerRow *self)
                 }
             }
         }
-      else if (!sp_capture_reader_skip (self->reader))
+      else if (!sp_capture_reader_skip (priv->reader))
         return;
     }
 
-  g_clear_pointer (&self->counters, g_hash_table_unref);
-  self->counters = new_data;
-}
-
-static inline gdouble
-calc_x (SpLineVisualizerRow *self,
-        gint64               time)
-{
-  gdouble ret = (gdouble)time / (gdouble)self->duration;
-  return ret;
+  g_clear_pointer (&priv->counters, g_hash_table_unref);
+  priv->counters = new_data;
 }
 
 static inline gdouble
@@ -191,8 +191,7 @@ calc_y (SpLineVisualizerRow   *self,
         LineData              *ld,
         SpCaptureCounterValue  value)
 {
-  gdouble ret = value.vdbl / 100.0;
-  return ret;
+  return value.vdbl / 100.0;
 }
 
 static gboolean
@@ -200,65 +199,56 @@ sp_line_visualizer_row_draw (GtkWidget *widget,
                              cairo_t   *cr)
 {
   SpLineVisualizerRow *self = (SpLineVisualizerRow *)widget;
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
   GtkAllocation alloc;
   GHashTableIter iter;
+  gdouble duration;
   gboolean ret;
   gpointer key, val;
-  guint i;
 
   g_assert (SP_IS_LINE_VISUALIZER_ROW (widget));
   g_assert (cr != NULL);
 
-  if (self->needs_recalc)
+  if (priv->needs_recalc)
     sp_line_visualizer_row_recalc (self);
 
   gtk_widget_get_allocation (widget, &alloc);
 
   ret = GTK_WIDGET_CLASS (sp_line_visualizer_row_parent_class)->draw (widget, cr);
 
-  cairo_save (cr);
+  duration = (gdouble)priv->duration;
 
-  g_hash_table_iter_init (&iter, self->counters);
+  g_hash_table_iter_init (&iter, priv->counters);
 
   while (g_hash_table_iter_next (&iter, &key, &val))
     {
       LineData *ld = val;
-      gdouble last_x = 0;
-      gdouble last_y = 0;
 
+      cairo_save (cr);
       cairo_move_to (cr, 0, alloc.height);
 
-      for (i = 0; i < ld->values->len; i++)
+      for (guint i = 0; i < ld->values->len; i++)
         {
           LineDataItem *item = &g_array_index (ld->values, LineDataItem, i);
           gdouble x;
           gdouble y;
 
-          x = calc_x (self, item->time) * alloc.width;
-          y = alloc.height - (calc_y (self, ld, item->value) * alloc.height);
-
-          //g_print ("x=%d y =%d\n", (int)x, (int)y);
+          x = (item->time / duration) * alloc.width;
+          y = alloc.height - ((item->value.vdbl / 100.0) * alloc.height);
 
           cairo_line_to (cr, x, y);
-
-          (void)last_x;
-          (void)last_y;
-
-          last_x = x;
-          last_y = x;
         }
 
       cairo_line_to (cr, alloc.width, alloc.height);
       cairo_line_to (cr, 0, alloc.height);
-      cairo_set_line_width (cr, 1.0);
-      cairo_set_source_rgba (cr, 0, 0, 0, 0.4);
+
+      SP_LINE_VISUALIZER_ROW_GET_CLASS (self)->prepare (self, cr, ld->id);
+
       cairo_stroke_preserve (cr);
-      cairo_set_source_rgba (cr, 0, 0, 0, 0.2);
       cairo_fill (cr);
+      cairo_restore (cr);
     }
 
-  cairo_restore (cr);
-
   return ret;
 }
 
@@ -267,37 +257,52 @@ sp_line_visualizer_row_set_reader (SpVisualizerRow *row,
                                    SpCaptureReader *reader)
 {
   SpLineVisualizerRow *self = (SpLineVisualizerRow *)row;
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
 
   g_assert (SP_IS_LINE_VISUALIZER_ROW (self));
 
-  if (self->reader != reader)
+  if (priv->reader != reader)
     {
-      g_clear_pointer (&self->reader, sp_capture_reader_unref);
-
-      if (reader)
-      {
-        self->reader = sp_capture_reader_ref (reader);
-        self->start_time = 0;
-        self->duration = 0;
-      }
+      if (priv->reader != NULL)
+        {
+          sp_capture_reader_unref (priv->reader);
+          priv->reader = NULL;
+          priv->start_time = 0;
+          priv->duration = 0;
+        }
 
-      /* TODO */
-      sp_line_visualizer_row_add_counter (self, 1);
-      sp_line_visualizer_row_add_counter (self, 3);
-      sp_line_visualizer_row_add_counter (self, 5);
-      sp_line_visualizer_row_add_counter (self, 7);
+      if (reader != NULL)
+        {
+          priv->reader = sp_capture_reader_ref (reader);
+          priv->start_time = 0;
+          priv->duration = 0;
+          priv->needs_recalc = TRUE;
+        }
 
       gtk_widget_queue_draw (GTK_WIDGET (self));
     }
 }
 
 static void
+sp_line_visualizer_row_real_prepare (SpLineVisualizerRow *self,
+                                     cairo_t             *cr,
+                                     guint                counter_id)
+{
+  g_assert (SP_IS_LINE_VISUALIZER_ROW (self));
+  g_assert (cr != NULL);
+
+  cairo_set_line_width (cr, 1.0);
+  cairo_set_source_rgba (cr, 0, 0, 0, 0.4);
+}
+
+static void
 sp_line_visualizer_row_finalize (GObject *object)
 {
   SpLineVisualizerRow *self = (SpLineVisualizerRow *)object;
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
 
-  g_clear_pointer (&self->counters, g_hash_table_unref);
-  g_clear_pointer (&self->reader, sp_capture_reader_unref);
+  g_clear_pointer (&priv->counters, g_hash_table_unref);
+  g_clear_pointer (&priv->reader, sp_capture_reader_unref);
 
   G_OBJECT_CLASS (sp_line_visualizer_row_parent_class)->finalize (object);
 }
@@ -309,11 +314,12 @@ sp_line_visualizer_row_get_property (GObject    *object,
                                      GParamSpec *pspec)
 {
   SpLineVisualizerRow *self = SP_LINE_VISUALIZER_ROW (object);
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
 
   switch (prop_id)
     {
     case PROP_TITLE:
-      g_object_get_property (G_OBJECT (self->label), "label", value);
+      g_object_get_property (G_OBJECT (priv->label), "label", value);
       break;
 
     default:
@@ -328,11 +334,12 @@ sp_line_visualizer_row_set_property (GObject      *object,
                                      GParamSpec   *pspec)
 {
   SpLineVisualizerRow *self = SP_LINE_VISUALIZER_ROW (object);
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
 
   switch (prop_id)
     {
     case PROP_TITLE:
-      g_object_set_property (G_OBJECT (self->label), "label", value);
+      g_object_set_property (G_OBJECT (priv->label), "label", value);
       break;
 
     default:
@@ -347,6 +354,8 @@ sp_line_visualizer_row_class_init (SpLineVisualizerRowClass *klass)
   GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
   SpVisualizerRowClass *visualizer_class = SP_VISUALIZER_ROW_CLASS (klass);
 
+  klass->prepare = sp_line_visualizer_row_real_prepare;
+
   object_class->finalize = sp_line_visualizer_row_finalize;
   object_class->get_property = sp_line_visualizer_row_get_property;
   object_class->set_property = sp_line_visualizer_row_set_property;
@@ -368,19 +377,21 @@ sp_line_visualizer_row_class_init (SpLineVisualizerRowClass *klass)
 static void
 sp_line_visualizer_row_init (SpLineVisualizerRow *self)
 {
-  PangoAttrList *attrs = NULL;
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
+  PangoAttrList *attrs = pango_attr_list_new ();
 
-  self->counters = g_hash_table_new (NULL, NULL);
+  priv->counters = g_hash_table_new (NULL, NULL);
 
-  attrs = pango_attr_list_new ();
   pango_attr_list_insert (attrs, pango_attr_scale_new (PANGO_SCALE_SMALL * PANGO_SCALE_SMALL));
-  self->label = g_object_new (GTK_TYPE_LABEL,
+
+  priv->label = g_object_new (GTK_TYPE_LABEL,
                               "attributes", attrs,
                               "visible", TRUE,
                               "xalign", 0.0f,
                               "yalign", 0.0f,
                               NULL);
-  gtk_container_add (GTK_CONTAINER (self), GTK_WIDGET (self->label));
+  gtk_container_add (GTK_CONTAINER (self), GTK_WIDGET (priv->label));
+
   pango_attr_list_unref (attrs);
 }
 
@@ -388,9 +399,28 @@ void
 sp_line_visualizer_row_add_counter (SpLineVisualizerRow *self,
                                     guint                counter_id)
 {
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
+
   g_assert (SP_IS_LINE_VISUALIZER_ROW (self));
+  g_assert (priv->counters != NULL);
+
+  g_hash_table_insert (priv->counters, GSIZE_TO_POINTER (counter_id), NULL);
+
+  if (SP_LINE_VISUALIZER_ROW_GET_CLASS (self)->counter_added)
+    SP_LINE_VISUALIZER_ROW_GET_CLASS (self)->counter_added (self, counter_id);
+
+  priv->needs_recalc = TRUE;
 
-  self->needs_recalc = TRUE;
-  g_hash_table_insert (self->counters, GSIZE_TO_POINTER (counter_id), NULL);
   gtk_widget_queue_draw (GTK_WIDGET (self));
 }
+
+void
+sp_line_visualizer_row_clear (SpLineVisualizerRow *self)
+{
+  SpLineVisualizerRowPrivate *priv = sp_line_visualizer_row_get_instance_private (self);
+
+  g_return_if_fail (SP_IS_LINE_VISUALIZER_ROW (self));
+
+  g_hash_table_remove_all (priv->counters);
+  gtk_widget_queue_resize (GTK_WIDGET (self));
+}
diff --git a/lib/sp-line-visualizer-row.h b/lib/sp-line-visualizer-row.h
index bf6aef8..61c5cf2 100644
--- a/lib/sp-line-visualizer-row.h
+++ b/lib/sp-line-visualizer-row.h
@@ -25,9 +25,38 @@ G_BEGIN_DECLS
 
 #define SP_TYPE_LINE_VISUALIZER_ROW (sp_line_visualizer_row_get_type())
 
-G_DECLARE_FINAL_TYPE (SpLineVisualizerRow, sp_line_visualizer_row, SP, LINE_VISUALIZER_ROW, SpVisualizerRow)
+G_DECLARE_DERIVABLE_TYPE (SpLineVisualizerRow, sp_line_visualizer_row, SP, LINE_VISUALIZER_ROW, 
SpVisualizerRow)
+
+struct _SpLineVisualizerRowClass
+{
+  SpVisualizerRowClass parent_class;
+
+  void (*counter_added) (SpLineVisualizerRow *self,
+                         guint                counter_id);
+  void (*prepare)       (SpLineVisualizerRow *self,
+                         cairo_t             *cr,
+                         guint                counter_id);
+
+  gpointer _reserved1;
+  gpointer _reserved2;
+  gpointer _reserved3;
+  gpointer _reserved4;
+  gpointer _reserved5;
+  gpointer _reserved6;
+  gpointer _reserved7;
+  gpointer _reserved8;
+  gpointer _reserved9;
+  gpointer _reserved10;
+  gpointer _reserved11;
+  gpointer _reserved12;
+  gpointer _reserved13;
+  gpointer _reserved14;
+  gpointer _reserved15;
+  gpointer _reserved16;
+};
 
 GtkWidget *sp_line_visualizer_row_new         (void);
+void       sp_line_visualizer_row_clear       (SpLineVisualizerRow *self);
 void       sp_line_visualizer_row_add_counter (SpLineVisualizerRow *self,
                                                guint                counter_id);
 
diff --git a/src/resources/ui/sp-window.ui b/src/resources/ui/sp-window.ui
index 1949bde..cd7cd00 100644
--- a/src/resources/ui/sp-window.ui
+++ b/src/resources/ui/sp-window.ui
@@ -172,7 +172,7 @@
                       <object class="GtkListBox" id="visualizer_rows">
                         <property name="visible">true</property>
                         <child>
-                          <object class="SpLineVisualizerRow" id="cpu_row">
+                          <object class="SpCpuVisualizerRow" id="cpu_row">
                             <property name="title" translatable="yes">CPU</property>
                             <property name="height-request">75</property>
                             <property name="selectable">false</property>