Add px/differential_flamegraph script

Signed-off-by: Dom Del Nano <ddelnano@gmail.com>
(cherry picked from commit 12881672c021e47a9090df3335c29f6048e99df3)

Author: ddelnano

src/pxl_scripts/px/differential_flamegraph/differential.pxl

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+# Copyright 2018- The Pixie Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import px
+
+def export_flame_graph(start_time: str, namespace: str, pod: str, baseline_pod: str):
+  stack_traces = px.DataFrame(table='stack_traces.beta', start_time=start_time)
+  stack_traces.namespace = stack_traces.ctx['namespace']
+  stack_traces = stack_traces[px.contains(stack_traces.namespace, namespace)]
+  stack_traces.node = px.Node(px._exec_hostname())
+  stack_traces.pod = stack_traces.ctx['pod']
+  stack_traces.keep_row = px.select(px.contains(stack_traces.pod, baseline_pod), True, False)
+  stack_traces.keep_row = px.select(stack_traces.keep_row or px.contains(stack_traces.pod, pod), True, False)
+  stack_traces = stack_traces[stack_traces.keep_row]
+
+  stack_traces = stack_traces.groupby(['node', 'namespace', 'pod', 'stack_trace_id']).agg(
+      stack_trace=('stack_trace', px.any),
+      count=('count', px.sum)
+  )
+
+  pod1 = stack_traces[px.contains(stack_traces.pod, baseline_pod)]
+  pod1 = pod1.drop(['node', 'namespace', 'pod', 'stack_trace_id'])
+
+  pod2 = stack_traces[px.contains(stack_traces.pod, pod)]
+  pod2 = pod2.drop(['node', 'namespace', 'pod', 'stack_trace_id'])
+
+  merged = pod1.merge(
+    pod2,
+    how='right',
+    left_on='stack_trace',
+    right_on='stack_trace'
+    suffixes=['_1', '_2'],
+  )
+  # Pixie's stack trace format permits spaces, but Brendan Gregg's scripts do not
+  merged.stack_trace_2 = px.replace(' ', merged.stack_trace_2, '')
+  merged.delta = merged.count_2 - merged.count_1
+  return merged[['stack_trace_2', 'count_1', 'count_2', 'delta']]

src/pxl_scripts/px/differential_flamegraph/manifest.yaml

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+---
+short: Differential Flame Graph
+long: >
+  This live view shows a differential CPU flame graph. This is helpful in identifying what code
+  paths have changed between deployments, different container instances, etc.

src/pxl_scripts/px/differential_flamegraph/vis.json

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+{
+    "variables": [
+        {
+            "name": "start_time",
+            "type": "PX_STRING",
+            "description": "The relative start time of the window. Current time is assumed to be now",
+            "defaultValue": "-5m"
+        },
+        {
+            "name": "namespace",
+            "type": "PX_NAMESPACE",
+            "description": "The namespace to filter on."
+        },
+        {
+            "name": "pod",
+            "type": "PX_POD",
+            "description": "The pod that will have its flamegraph analyzed compared to the baseline_pod"
+        },
+        {
+            "name": "baseline_pod",
+            "type": "PX_POD",
+            "description": "The pod to serve as the baseline. The resulting flamegraph will show the difference from this pod's profile."
+        }
+    ],
+    "globalFuncs": [],
+    "widgets": [
+        {
+            "name": "Flamegraph",
+            "position": {
+                "x": 0,
+                "y": 0,
+                "w": 12,
+                "h": 6
+            },
+            "func": {
+                "name": "export_flame_graph",
+                "args": [
+                    {
+                        "name": "start_time",
+                        "variable": "start_time"
+                    },
+                    {
+                        "name": "namespace",
+                        "variable": "namespace"
+                    },
+                    {
+                        "name": "pod",
+                        "variable": "pod"
+                    },
+                    {
+                        "name": "baseline_pod",
+                        "variable": "baseline_pod"
+                    }
+                ]
+            },
+            "displaySpec": {
+                "@type": "types.px.dev/px.vispb.StackTraceFlameGraph",
+                "stacktraceColumn": "stack_trace_2",
+                "countColumn": "count_2",
+                "differenceColumn": "delta"
+            }
+        }
+    ]
+}