perf jevents metric: Add ability to rewrite metrics in terms of others

Add RewriteMetricsInTermsOfOthers that iterates over pairs of names and
expressions trying to replace an expression, within the current
expression, with its name.

Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Caleb Biggers <caleb.biggers@intel.com>
Cc: Florian Fischer <florian.fischer@muhq.space>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kang Minchul <tegongkang@gmail.com>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Perry Taylor <perry.taylor@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linuxppc-dev@lists.ozlabs.org
Link: https://lore.kernel.org/r/20230126233645.200509-3-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/pmu-events/metric.py

@@ -4,7 +4,7 @@ import ast
 import decimal
 import json
 import re
-from typing import Dict, List, Optional, Set, Union
+from typing import Dict, List, Optional, Set, Tuple, Union
 
 
 class Expression:
@@ -26,6 +26,9 @@ class Expression:
     """Returns true when two expressions are the same."""
     raise NotImplementedError()
 
+  def Substitute(self, name: str, expression: 'Expression') -> 'Expression':
+    raise NotImplementedError()
+
   def __str__(self) -> str:
     return self.ToPerfJson()
 
@@ -186,6 +189,15 @@ class Operator(Expression):
           other.lhs) and self.rhs.Equals(other.rhs)
     return False
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    if self.Equals(expression):
+      return Event(name)
+    lhs = self.lhs.Substitute(name, expression)
+    rhs = None
+    if self.rhs:
+      rhs = self.rhs.Substitute(name, expression)
+    return Operator(self.operator, lhs, rhs)
+
 
 class Select(Expression):
   """Represents a select ternary in the parse tree."""
@@ -225,6 +237,14 @@ class Select(Expression):
           other.false_val) and self.true_val.Equals(other.true_val)
     return False
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    if self.Equals(expression):
+      return Event(name)
+    true_val = self.true_val.Substitute(name, expression)
+    cond = self.cond.Substitute(name, expression)
+    false_val = self.false_val.Substitute(name, expression)
+    return Select(true_val, cond, false_val)
+
 
 class Function(Expression):
   """A function in an expression like min, max, d_ratio."""
@@ -267,6 +287,15 @@ class Function(Expression):
       return result
     return False
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    if self.Equals(expression):
+      return Event(name)
+    lhs = self.lhs.Substitute(name, expression)
+    rhs = None
+    if self.rhs:
+      rhs = self.rhs.Substitute(name, expression)
+    return Function(self.fn, lhs, rhs)
+
 
 def _FixEscapes(s: str) -> str:
   s = re.sub(r'([^\\]),', r'\1\\,', s)
@@ -293,6 +322,9 @@ class Event(Expression):
   def Equals(self, other: Expression) -> bool:
     return isinstance(other, Event) and self.name == other.name
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    return self
+
 
 class Constant(Expression):
   """A constant within the expression tree."""
@@ -317,6 +349,9 @@ class Constant(Expression):
   def Equals(self, other: Expression) -> bool:
     return isinstance(other, Constant) and self.value == other.value
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    return self
+
 
 class Literal(Expression):
   """A runtime literal within the expression tree."""
@@ -336,6 +371,9 @@ class Literal(Expression):
   def Equals(self, other: Expression) -> bool:
     return isinstance(other, Literal) and self.value == other.value
 
+  def Substitute(self, name: str, expression: Expression) -> Expression:
+    return self
+
 
 def min(lhs: Union[int, float, Expression], rhs: Union[int, float,
                                                        Expression]) -> Function:
@@ -461,6 +499,7 @@ class MetricGroup:
 
 
 class _RewriteIfExpToSelect(ast.NodeTransformer):
+  """Transformer to convert if-else nodes to Select expressions."""
 
   def visit_IfExp(self, node):
     # pylint: disable=invalid-name
@@ -498,7 +537,37 @@ def ParsePerfJson(orig: str) -> Expression:
   for kw in keywords:
     py = re.sub(rf'Event\(r"{kw}"\)', kw, py)
 
-  parsed = ast.parse(py, mode='eval')
+  try:
+    parsed = ast.parse(py, mode='eval')
+  except SyntaxError as e:
+    raise SyntaxError(f'Parsing expression:\n{orig}') from e
   _RewriteIfExpToSelect().visit(parsed)
   parsed = ast.fix_missing_locations(parsed)
   return _Constify(eval(compile(parsed, orig, 'eval')))
+
+
+def RewriteMetricsInTermsOfOthers(metrics: List[Tuple[str, Expression]]
+                                  )-> Dict[str, Expression]:
+  """Shorten metrics by rewriting in terms of others.
+
+  Args:
+    metrics (list): pairs of metric names and their expressions.
+  Returns:
+    Dict: mapping from a metric name to a shortened expression.
+  """
+  updates: Dict[str, Expression] = dict()
+  for outer_name, outer_expression in metrics:
+    updated = outer_expression
+    while True:
+      for inner_name, inner_expression in metrics:
+        if inner_name.lower() == outer_name.lower():
+          continue
+        if inner_name in updates:
+          inner_expression = updates[inner_name]
+        updated = updated.Substitute(inner_name, inner_expression)
+      if updated.Equals(outer_expression):
+        break
+      if outer_name in updates and updated.Equals(updates[outer_name]):
+        break
+      updates[outer_name] = updated
+  return updates

tools/perf/pmu-events/metric_test.py

@@ -2,7 +2,9 @@
 import unittest
 from metric import Constant
 from metric import Event
+from metric import Expression
 from metric import ParsePerfJson
+from metric import RewriteMetricsInTermsOfOthers
 
 
 class TestMetricExpressions(unittest.TestCase):
@@ -153,5 +155,13 @@ class TestMetricExpressions(unittest.TestCase):
     after = '0 * SLOTS'
     self.assertEqual(ParsePerfJson(before).Simplify().ToPerfJson(), after)
 
+  def test_RewriteMetricsInTermsOfOthers(self):
+    Expression.__eq__ = lambda e1, e2: e1.Equals(e2)
+    before = [('m1', ParsePerfJson('a + b + c + d')),
+              ('m2', ParsePerfJson('a + b + c'))]
+    after = {'m1': ParsePerfJson('m2 + d')}
+    self.assertEqual(RewriteMetricsInTermsOfOthers(before), after)
+    Expression.__eq__ = None
+
 if __name__ == '__main__':
   unittest.main()