Introduce cost threshold for flamegraph to minimize memory overhead.

For larger data files, the flamegraph can easily consume hundreds
of megabytes of ram and take multiple seconds to be build up. This
is mostly due to the dozens of small leaf items, all of which only
have tiny cost and will not be shown most of the time.

The new default cut-off of 0.1% drastically reduces the memory
overhead and the flamegraph will be build nearly instantly even for
larger data sets.

In the future, one could even refine the data on-demand.

diff --git a/gui/flamegraph.cpp b/gui/flamegraph.cpp
index b8e62bf..3903e58 100644 (file)
--- a/gui/flamegraph.cpp
+++ b/gui/flamegraph.cpp
@@ -33,6 +33,7 @@
 #include <QAction>
 #include <QComboBox>
 #include <QCheckBox>
+#include <QDoubleSpinBox>
 
 #include <ThreadWeaver/ThreadWeaver>
 #include <KLocalizedString>
@@ -242,7 +243,8 @@ FrameGraphicsItem* findItemByFunction(const QList<QGraphicsItem*>& items, const
 /**
  * Convert the top-down graph into a tree of FrameGraphicsItem.
  */
-void toGraphicsItems(const QVector<RowData>& data, FrameGraphicsItem *parent, uint64_t AllocationData::* member)
+void toGraphicsItems(const QVector<RowData>& data, FrameGraphicsItem *parent, uint64_t AllocationData::* member,
+                     const double costThreshold)
 {
     foreach (const auto& row, data) {
         auto item = findItemByFunction(parent->childItems(), row.location->function);
@@ -253,7 +255,9 @@ void toGraphicsItems(const QVector<RowData>& data, FrameGraphicsItem *parent, ui
         } else {
             item->setCost(item->cost() + row.cost.*member);
         }
-        toGraphicsItems(row.children, item, member);
+        if (item->cost() > costThreshold) {
+            toGraphicsItems(row.children, item, member, costThreshold);
+        }
     }
 }
 
@@ -274,7 +278,7 @@ uint64_t AllocationData::* memberForType(CostType type)
     Q_UNREACHABLE();
 }
 
-FrameGraphicsItem* parseData(const QVector<RowData>& topDownData, CostType type)
+FrameGraphicsItem* parseData(const QVector<RowData>& topDownData, CostType type, double costThreshold)
 {
     uint64_t AllocationData::* member = memberForType(type);
 
@@ -308,7 +312,7 @@ FrameGraphicsItem* parseData(const QVector<RowData>& topDownData, CostType type)
     auto rootItem = new FrameGraphicsItem(totalCost, type, label);
     rootItem->setBrush(scheme.background());
     rootItem->setPen(pen);
-    toGraphicsItems(topDownData, rootItem, member);
+    toGraphicsItems(topDownData, rootItem, member, totalCost * costThreshold / 100.);
     return rootItem;
 }
 
@@ -339,16 +343,36 @@ FlameGraph::FlameGraph(QWidget* parent, Qt::WindowFlags flags)
     m_view->viewport()->setMouseTracking(true);
     m_view->setFont(QFont(QStringLiteral("monospace")));
     m_view->setContextMenuPolicy(Qt::ActionsContextMenu);
+
     auto bottomUpCheckbox = new QCheckBox(i18n("Bottom-Down View"), this);
     connect(bottomUpCheckbox, &QCheckBox::toggled, this, [this, bottomUpCheckbox] {
         m_showBottomUpData = bottomUpCheckbox->isChecked();
         showData();
     });
 
+    auto costThreshold = new QDoubleSpinBox(this);
+    costThreshold->setDecimals(2);
+    costThreshold->setMinimum(0);
+    costThreshold->setMaximum(99.90);
+    costThreshold->setPrefix(i18n("Cost Threshold: "));
+    costThreshold->setSuffix(QStringLiteral("%"));
+    costThreshold->setValue(m_costThreshold);
+    costThreshold->setSingleStep(0.01);
+    costThreshold->setToolTip(i18n("<qt>The cost threshold defines a fractional cut-off value. "
+                                   "Items with a relative cost below this value will not be shown in the flame graph. "
+                                   "This is done as an optimization to quickly generate graphs for large data set with "
+                                   "low memory overhead. If you need more details, decrease the threshold value, or set it to zero.</qt>"));
+    connect(costThreshold, static_cast<void (QDoubleSpinBox::*) (double)>(&QDoubleSpinBox::valueChanged),
+            this, [this] (double threshold) {
+                m_costThreshold = threshold;
+                showData();
+            });
+
     auto controls = new QWidget(this);
     controls->setLayout(new QHBoxLayout);
     controls->layout()->addWidget(m_costSource);
     controls->layout()->addWidget(bottomUpCheckbox);
+    controls->layout()->addWidget(costThreshold);
 
     setLayout(new QVBoxLayout);
     layout()->addWidget(controls);
@@ -399,8 +423,9 @@ void FlameGraph::showData()
     using namespace ThreadWeaver;
     auto data = m_showBottomUpData ? m_bottomUpData : m_topDownData;
     auto source = m_costSource->currentData().value<CostType>();
-    stream() << make_job([data, source, this]() {
-        auto parsedData = parseData(data, source);
+    auto threshold = m_costThreshold;
+    stream() << make_job([data, source, threshold, this]() {
+        auto parsedData = parseData(data, source, threshold);
         QMetaObject::invokeMethod(this, "setData", Qt::QueuedConnection,
                                   Q_ARG(FrameGraphicsItem*, parsedData));
     });

diff --git a/gui/flamegraph.h b/gui/flamegraph.h
index 1997c8c..72555d2 100644 (file)
--- a/gui/flamegraph.h
+++ b/gui/flamegraph.h
@@ -59,6 +59,8 @@ private:
     FrameGraphicsItem* m_selectedItem;
     int m_minRootWidth;
     bool m_showBottomUpData = false;
+    // cost threshold in percent, items below that value will not be shown
+    double m_costThreshold = 0.1;
 };
 
 #endif // FLAMEGRAPH_H