Rebenchmark configs to avoid noise

stack-info: PR: #654, branch: jansel/stack/146

Author: jansel

helion/autotuner/base_search.py

@@ -15,9 +15,12 @@
 import sys
 import time
 from typing import TYPE_CHECKING
+from typing import Callable
 from typing import NamedTuple
 from typing import NoReturn
 
+from .benchmarking import interleaved_bench
+
 if TYPE_CHECKING:
     from triton.runtime.jit import JITFunction
 
@@ -90,6 +93,7 @@ def __init__(self, kernel: BoundKernel, args: Sequence[object]) -> None:
         self.args: Sequence[object] = args
         self.counters: collections.Counter[str] = collections.Counter()
         self.log = LambdaLogger(self.settings.autotune_log_level)
+        self.best_perf_so_far = inf
         seed = self.settings.autotune_random_seed
         random.seed(seed)
         self.log(f"Autotune random seed: {seed}")
@@ -167,7 +171,7 @@ def _validate_against_baseline(
             return False
         return True
 
-    def benchmark(self, config: Config) -> float:
+    def benchmark(self, config: Config) -> tuple[Callable[..., object], float]:
         """
         Benchmark a specific configuration.
 
@@ -177,12 +181,12 @@ def benchmark(self, config: Config) -> float:
             config: The configuration to benchmark.
 
         Returns:
-            The performance of the configuration in seconds.
+            The function and performance of the configuration in ms.
         """
         fn = self.kernel.compile_config(config, allow_print=False)
         if self.start_precompile_and_check_for_hangs(config, fn)():
-            return self.benchmark_function(config, fn)
-        return inf
+            return fn, self.benchmark_function(config, fn)
+        return fn, inf
 
     def benchmark_function(self, config: Config, fn: CompiledConfig) -> float:
         """
@@ -194,7 +198,7 @@ def benchmark_function(self, config: Config, fn: CompiledConfig) -> float:
             fn: A precompiled version of config.
 
         Returns:
-            The performance of the configuration in seconds.
+            The performance of the configuration in ms.
         """
         self.counters["benchmark"] += 1
         self.log.debug(lambda: f"Running benchmark for {config!r}")
@@ -216,10 +220,13 @@ def benchmark_function(self, config: Config, fn: CompiledConfig) -> float:
                 return_mode="median",
             )
             t2 = time.perf_counter()
+            assert isinstance(res, float)
             self.log.debug(
                 lambda: f"result: {res:.4f}ms (took {t1 - t0:.1f}s + {t2 - t1:.1f}s)",
             )
-            return res  # pyright: ignore[reportReturnType]
+            if res < self.best_perf_so_far:
+                self.best_perf_so_far = res
+            return res
         except Exception as e:
             action = classify_triton_exception(e)
             if action == "raise":
@@ -286,7 +293,9 @@ def extract_launcher(
             timeout=self.settings.autotune_compile_timeout,
         )
 
-    def parallel_benchmark(self, configs: list[Config]) -> list[tuple[Config, float]]:
+    def parallel_benchmark(
+        self, configs: list[Config]
+    ) -> list[tuple[Config, Callable[..., object], float]]:
         """
         Benchmark multiple configurations in parallel.
 
@@ -312,9 +321,9 @@ def parallel_benchmark(self, configs: list[Config]) -> list[tuple[Config, float]
         for config, fn, is_working in zip(configs, fns, is_workings, strict=True):
             if is_working:
                 # benchmark one-by-one to avoid noisy results
-                results.append((config, self.benchmark_function(config, fn)))
+                results.append((config, fn, self.benchmark_function(config, fn)))
             else:
-                results.append((config, inf))
+                results.append((config, fn, inf))
         return results
 
     def autotune(self) -> Config:
@@ -361,15 +370,20 @@ class PopulationMember(NamedTuple):
     Represents a member of the population in population-based search algorithms.
 
     Attributes:
-        perf (float): The performance of the configuration.
+        perfs (list[float]): The performance of the configuration, accumulated over multiple benchmarks.
         flat_values (FlatConfig): The flat representation of the configuration values.
         config (Config): The full configuration object.
     """
 
-    perf: float
+    fn: Callable[..., object]
+    perfs: list[float]
     flat_values: FlatConfig
     config: Config
 
+    @property
+    def perf(self) -> float:
+        return self.perfs[-1]
+
 
 def performance(member: PopulationMember) -> float:
     """
@@ -430,7 +444,8 @@ def benchmark_flat(self, flat_values: FlatConfig) -> PopulationMember:
             A population member with the benchmark results.
         """
         config = self.config_gen.unflatten(flat_values)
-        return PopulationMember(self.benchmark(config), flat_values, config)
+        fn, perf = self.benchmark(config)
+        return PopulationMember(fn, [perf], flat_values, config)
 
     def parallel_benchmark_flat(
         self, to_check: list[FlatConfig]
@@ -446,13 +461,65 @@ def parallel_benchmark_flat(
         """
         configs = [*map(self.config_gen.unflatten, to_check)]
         result = []
-        for flat_values, config_in, (config_out, perf) in zip(
+        for flat_values, config_in, (config_out, fn, perf) in zip(
             to_check, configs, self.parallel_benchmark(configs), strict=True
         ):
             assert config_in is config_out
-            result.append(PopulationMember(perf, flat_values, config_in))
+            result.append(PopulationMember(fn, [perf], flat_values, config_in))
         return result
 
+    def compare(self, a: PopulationMember, b: PopulationMember) -> int:
+        """
+        Compare two population members based on their performance, possibly with re-benchmarking.
+
+        Args:
+            a: The first population member.
+            b: The second population member.
+
+        Returns:
+            -1 if a is better than b, 1 if b is better than a, 0 if they are equal.
+        """
+        if self.should_rebenchmark(a) and self.should_rebenchmark(b):
+            self.rebenchmark([a, b])
+        return (a.perf > b.perf) - (a.perf < b.perf)
+
+    def should_rebenchmark(self, member: PopulationMember) -> bool:
+        """
+        Determine if a population member should be re-benchmarked to avoid outliers.
+
+        Args:
+            member: The population member to check.
+
+        Returns:
+            True if the member should be re-benchmarked, False otherwise.
+        """
+        return (
+            member.perf
+            < self.settings.autotune_rebenchmark_threshold * self.best_perf_so_far
+            and math.isfinite(member.perf)
+        )
+
+    def rebenchmark(self, members: list[PopulationMember]) -> None:
+        """
+        Re-benchmark a list of population members to avoid outliers.
+        """
+        if len(members) < 2:
+            return
+        repeat = max(3, int(200 / self.best_perf_so_far))
+        new_timings = interleaved_bench(
+            [functools.partial(m.fn, *self.args) for m in members], repeat=repeat
+        )
+        for m, t in zip(members, new_timings, strict=True):
+            m.perfs.append(t)
+            if t < self.best_perf_so_far:
+                self.best_perf_so_far = t
+
+    def rebenchmark_population(self) -> None:
+        """
+        Re-benchmark the entire population to avoid outliers.
+        """
+        self.rebenchmark([p for p in self.population if self.should_rebenchmark(p)])
+
     def statistics(self) -> str:
         """
         Generate statistics for the current population.

helion/autotuner/benchmarking.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import functools
+import statistics
+from typing import Callable
+
+from triton import runtime
+
+
+def interleaved_bench(fns: list[Callable[[], object]], *, repeat: int) -> list[float]:
+    """
+    Benchmark multiple functions at once, interleaving their executions to reduce
+    the impact of external factors (e.g., load, temperature) on the
+    measurements.
+    """
+    # warmup
+    for fn in fns:
+        fn()
+    clear_cache = functools.partial(
+        runtime.driver.active.clear_cache,  # type: ignore[attr-defined]
+        runtime.driver.active.get_empty_cache_for_benchmark(),  # type: ignore[attr-defined]
+    )
+    clear_cache()
+    di = runtime.driver.active.get_device_interface()  # type: ignore[attr-defined]
+    start_events = [
+        [di.Event(enable_timing=True) for _ in range(repeat)] for _ in range(len(fns))
+    ]
+    end_events = [
+        [di.Event(enable_timing=True) for _ in range(repeat)] for _ in range(len(fns))
+    ]
+
+    di.synchronize()
+    for i in range(repeat):
+        for j in range(len(fns)):
+            clear_cache()
+            start_events[j][i].record()
+            fns[j]()
+            end_events[j][i].record()
+    di.synchronize()
+
+    return [
+        statistics.median(
+            [
+                s.elapsed_time(e)
+                for s, e in zip(start_events[j], end_events[j], strict=True)
+            ]
+        )
+        for j in range(len(fns))
+    ]

helion/autotuner/differential_evolution.py

@@ -81,7 +81,7 @@ def iter_candidates(self) -> Iterator[tuple[int, PopulationMember]]:
     def evolve_population(self) -> int:
         replaced = 0
         for i, candidate in self.iter_candidates():
-            if candidate.perf < self.population[i].perf:
+            if self.compare(candidate, self.population[i]) < 0:
                 self.population[i] = candidate
                 replaced += 1
         return replaced
@@ -97,4 +97,5 @@ def _autotune(self) -> Config:
         for i in range(2, self.num_generations):
             replaced = self.evolve_population()
             self.log(f"Generation {i}: replaced={replaced}", self.statistics)
+        self.rebenchmark_population()
         return self.best.config

helion/autotuner/finite_search.py

@@ -35,7 +35,7 @@ def __init__(
     def _autotune(self) -> Config:
         best_config = None
         best_time = float("inf")
-        for config, time in self.parallel_benchmark(self.configs):
+        for config, _fn, time in self.parallel_benchmark(self.configs):
             if time < best_time:
                 best_time = time
                 best_config = config

helion/runtime/settings.py

@@ -101,6 +101,9 @@ class _Settings:
     autotune_accuracy_check: bool = (
         os.environ.get("HELION_AUTOTUNE_ACCURACY_CHECK", "1") == "1"
     )
+    autotune_rebenchmark_threshold: float = float(
+        os.environ.get("HELION_REBENCHMARK_THRESHOLD", "1.5")
+    )
     print_output_code: bool = os.environ.get("HELION_PRINT_OUTPUT_CODE", "0") == "1"
     force_autotune: bool = os.environ.get("HELION_FORCE_AUTOTUNE", "0") == "1"
     allow_warp_specialize: bool = (
@@ -131,6 +134,7 @@ class Settings(_Settings):
         "autotune_precompile_jobs": "Maximum concurrent Triton precompile processes, default to cpu count.",
         "autotune_random_seed": "Seed used for autotuner random number generation. Defaults to HELION_AUTOTUNE_RANDOM_SEED or a time-based seed.",
         "autotune_accuracy_check": "If True, validate candidate configs against the baseline kernel output before accepting them during autotuning.",
+        "autotune_rebenchmark_threshold": "If a config is within threshold*best_perf, re-benchmark it to avoid outliers. Default is 1.5x.  Set to <1 to disable.",
         "print_output_code": "If True, print the output code of the kernel to stderr.",
         "force_autotune": "If True, force autotuning even if a config is provided.",
         "allow_warp_specialize": "If True, allow warp specialization for tl.range calls on CUDA devices.",