[2/2] Add differential flamegraph script (#2044)

Summary: Add differential flamegraph script

This depends on #2043.

Relevant Issues: N/A

Type of change: /kind new-pxl-script

Test Plan: Ran the local UI and verified that the non negated version
works as expected

![differential](https://github.com/user-attachments/assets/e021d5f6-e3e2-4d5c-a3a6-17612695e429)

Changelog Message: Add `px/differential_flamegraph` script for comparing
flamegraphs profiles between pods. See [this
post](https://www.brendangregg.com/blog/2014-11-09/differential-flame-graphs.html)
for more background on how to use a differential flamegraph.

---------

Signed-off-by: Dom Del Nano <ddelnano@gmail.com>

Author: ddelnano

src/pxl_scripts/px/differential_flamegraph/differential.pxl

@@ -0,0 +1,77 @@
+# 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
+
+negate = False
+# TODO(ddelnano): negation requires switching the type of join from right to left
+# or returning a different DataFrame. This might not be possible with pxl's current
+# functionality, but this should be implemented once it's possible.
+
+def merge_and_compute_delta(pod1, pod2, negate: bool):
+
+  diff = pod1.merge(
+    pod2,
+    how='right',
+    left_on='stack_trace',
+    right_on='stack_trace'
+    suffixes=['_1', '_2'],
+  )
+  # TODO(ddelnano): This needs to be switched with pod1 if the flamegraph should
+  # be negated.
+  percentage_agg = pod2.groupby(['pod']).agg(
+    count=('count', px.sum),
+  )
+  diff.pod = px.select(negate, diff.pod_1, diff.pod_2)
+  diff.stack_trace = px.select(negate, diff.stack_trace_1, diff.stack_trace_2)
+  diff.stack_trace = px.replace(' ', diff.stack_trace, '')
+  diff.count = px.select(negate, diff.count_1, diff.count_2)
+  diff.delta = diff.count_2 - diff.count_1
+  diff.delta = px.select(negate, px.negate(diff.delta), diff.delta)
+
+  merged = diff.merge(
+    percentage_agg,
+    how='inner',
+    left_on='pod',
+    right_on='pod',
+    suffixes=['', '_x']
+  )
+  merged.percent = 100 * merged.count / merged.count_x
+  return merged
+
+def differential_flamegraph(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[stack_traces.namespace == namespace]
+  stack_traces.node = px.Node(px._exec_hostname())
+  stack_traces.pod = stack_traces.ctx['pod']
+  stack_traces.keep_row = stack_traces.pod == baseline_pod
+  stack_traces.keep_row = px.select(stack_traces.keep_row or 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[stack_traces.pod == baseline_pod]
+  pod1 = pod1.drop(['node', 'namespace', 'stack_trace_id'])
+
+  pod2 = stack_traces[stack_traces.pod == pod]
+  pod2 = pod2.drop(['node', 'namespace', 'stack_trace_id'])
+
+  merged = merge_and_compute_delta(pod1, pod2, negate)
+  return merged[['stack_trace', 'count', 'delta', 'percent', 'pod']]

src/pxl_scripts/px/differential_flamegraph/manifest.yaml

@@ -0,0 +1,5 @@
+---
+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

@@ -0,0 +1,66 @@
+{
+    "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": "differential_flamegraph",
+                "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",
+                "countColumn": "count",
+                "percentageColumn": "percent",
+                "podColumn": "pod",
+                "differenceColumn": "delta"
+            }
+        }
+    ]
+}