From e4057575c7134321ac0d2b676babc8d48e299787 Mon Sep 17 00:00:00 2001
From: Allison Piper <alliepiper16@gmail.com>
Date: Thu, 24 Apr 2025 22:48:35 +0000
Subject: [PATCH] Disable throttling when `sync` exec tag is used.

---
 docs/cli_help.md                | 5 ++++-
 nvbench/detail/measure_cold.cu  | 3 ++-
 nvbench/detail/measure_cold.cuh | 5 +++--
 nvbench/detail/state_exec.cuh   | 4 +++-
 4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/docs/cli_help.md b/docs/cli_help.md
index 336a826..6021e0e 100644
--- a/docs/cli_help.md
+++ b/docs/cli_help.md
@@ -135,13 +135,16 @@
 
 * `--throttle-threshold <value>`
   * Set the GPU throttle threshold as percentage of the device's default clock rate.
-  * Default is 75%.
+  * Default is 75.
+  * Set to 0 to disable throttle detection entirely.
+  * Note that throttling is disabled when `nvbench::exec_tag::sync` is used.
   * Applies to the most recent `--benchmark`, or all benchmarks if specified
     before any `--benchmark` arguments.
 
 * `--throttle-recovery-delay <value>`
   * Set the GPU throttle recovery delay in seconds.
   * Default is 0.05 seconds.
+  * Note that throttling is disabled when `nvbench::exec_tag::sync` is used.
   * Applies to the most recent `--benchmark`, or all benchmarks if specified
     before any `--benchmark` arguments.
 
diff --git a/nvbench/detail/measure_cold.cu b/nvbench/detail/measure_cold.cu
index 5e1c6c2..6f0f5dd 100644
--- a/nvbench/detail/measure_cold.cu
+++ b/nvbench/detail/measure_cold.cu
@@ -43,6 +43,7 @@ measure_cold_base::measure_cold_base(state &exec_state)
         exec_state.get_stopping_criterion())}
     , m_disable_blocking_kernel{exec_state.get_disable_blocking_kernel()}
     , m_run_once{exec_state.get_run_once()}
+    , m_check_throttling(!exec_state.get_run_once() && exec_state.get_throttle_threshold() > 0.f)
     , m_min_samples{exec_state.get_min_samples()}
     , m_skip_time{exec_state.get_skip_time()}
     , m_timeout{exec_state.get_timeout()}
@@ -94,7 +95,7 @@ void measure_cold_base::run_trials_prologue() { m_walltime_timer.start(); }
 
 void measure_cold_base::record_measurements()
 {
-  if (!m_run_once)
+  if (m_check_throttling)
   {
     const auto current_clock_rate = m_gpu_frequency.get_clock_frequency();
     const auto default_clock_rate =
diff --git a/nvbench/detail/measure_cold.cuh b/nvbench/detail/measure_cold.cuh
index 93bff0f..e3b329d 100644
--- a/nvbench/detail/measure_cold.cuh
+++ b/nvbench/detail/measure_cold.cuh
@@ -95,6 +95,7 @@ protected:
 
   bool m_disable_blocking_kernel{false};
   bool m_run_once{false};
+  bool m_check_throttling;
 
   nvbench::int64_t m_min_samples{};
 
@@ -142,7 +143,7 @@ struct measure_cold_base::kernel_launch_timer
     {
       m_measure.block_stream();
     }
-    if (!m_measure.m_run_once)
+    if (m_measure.m_check_throttling)
     {
       m_measure.gpu_frequency_start();
     }
@@ -161,7 +162,7 @@ struct measure_cold_base::kernel_launch_timer
       m_measure.m_cpu_timer.start();
       m_measure.unblock_stream();
     }
-    if (!m_measure.m_run_once)
+    if (m_measure.m_check_throttling)
     {
       m_measure.gpu_frequency_stop();
     }
diff --git a/nvbench/detail/state_exec.cuh b/nvbench/detail/state_exec.cuh
index a0311d8..bf4fb9e 100644
--- a/nvbench/detail/state_exec.cuh
+++ b/nvbench/detail/state_exec.cuh
@@ -101,10 +101,12 @@ void state::exec(ExecTags tags, KernelLauncher &&kernel_launcher)
                              "`set_is_cpu_only(true)` is NOT called when defining the benchmark.");
   }
 
-  // Syncing will cause the blocking kernel pattern to deadlock:
   if constexpr (modifier_tags & sync)
   {
+    // Syncing will cause the blocking kernel pattern to deadlock:
     this->set_disable_blocking_kernel(true);
+    // Syncing will cause the throttle frequency measurements to be skewed heavily:
+    this->set_throttle_threshold(0.f);
   }
 
   if (this->is_skipped())