diff --git a/lib/gpio/diagnostics.ex b/lib/gpio/diagnostics.ex
index 9d7ecb5..3810d79 100644
--- a/lib/gpio/diagnostics.ex
+++ b/lib/gpio/diagnostics.ex
@@ -12,6 +12,7 @@ defmodule Circuits.GPIO.Diagnostics do
   to work on some devices.
   """
   alias Circuits.GPIO
+  alias Circuits.GPIO.Diagnostics.CPU
 
   @doc """
   Reminder for how to use report/2
@@ -55,14 +56,23 @@ defmodule Circuits.GPIO.Diagnostics do
       Input ids:   #{inspect(in_identifiers)}
       Backend: #{inspect(Circuits.GPIO.backend_info()[:name])}
 
+      == Functionality ==
+
       """,
       Enum.map(results, &pass_text/1),
       """
 
-      write/2:     #{round(speed_results.write_cps)} calls/s
-      read/1:      #{round(speed_results.read_cps)} calls/s
-      write_one/3: #{round(speed_results.write_one_cps)} calls/s
-      read_one/2:  #{round(speed_results.read_one_cps)} calls/s
+      == Performance ==
+
+      Kernel:      #{speed_results.uname}
+      CPU count:   #{speed_results.cpu_count}
+      CPU speed:   #{:erlang.float_to_binary(speed_results.speed_mhz, decimals: 1)} MHz
+      Warnings?:   #{speed_results.warnings?}
+
+      write/2:     #{cps_to_us(speed_results.write_cps)} µs/call
+      read/1:      #{cps_to_us(speed_results.read_cps)} µs/call
+      write_one/3: #{cps_to_us(speed_results.write_one_cps)} µs/call
+      read_one/2:  #{cps_to_us(speed_results.read_one_cps)} µs/call
 
       """,
       if(check_connections?,
@@ -81,6 +91,9 @@ defmodule Circuits.GPIO.Diagnostics do
     passed
   end
 
+  # Truncate sub-nanosecond for readability
+  defp cps_to_us(cps), do: :erlang.float_to_binary(1_000_000 / cps, decimals: 3)
+
   defp pass_text({name, :ok}), do: [name, ": ", :green, "PASSED", :reset, "\n"]
 
   defp pass_text({name, {:error, reason}}),
@@ -108,17 +121,29 @@ defmodule Circuits.GPIO.Diagnostics do
   @doc """
   Run GPIO API performance tests
 
-  Disclaimer: There should be a better way than relying on the Circuits.GPIO
-  write performance on nearly every device. Write performance shouldn't be
-  terrible, though.
+  If you get warnings about the CPU speed, run
+  `Circuits.GPIO.Diagnostics.CPU.force_slowest/0` or
+  `Circuits.GPIO.Diagnostics.CPU.set_speed/1` to make sure that the CPU doesn't
+  change speeds during the test.
+
+  Disclaimer: This tests Circuits.GPIO write performance. Write performance
+  should be reasonably good. However, if it's not acceptable, please
+  investigate other options. Usually there's some hardware-assisted way to
+  accomplish high speed GPIO tasks (PWM controllers, for example).
   """
   @spec speed_test(GPIO.gpio_spec()) :: %{
           write_cps: float(),
           read_cps: float(),
           write_one_cps: float(),
-          read_one_cps: float()
+          read_one_cps: float(),
+          uname: String.t(),
+          cpu_count: non_neg_integer(),
+          speed_mhz: number(),
+          warnings?: boolean()
         }
   def speed_test(gpio_spec) do
+    cpu_info = CPU.check_benchmark_suitability()
+
     times = 1000
     one_times = ceil(times / 100)
 
@@ -133,12 +158,14 @@ defmodule Circuits.GPIO.Diagnostics do
     write_one_cps = time_fun2(one_times, &write_one2/1, gpio_spec)
     read_one_cps = time_fun2(one_times, &read_one2/1, gpio_spec)
 
-    %{
+    results = %{
       write_cps: write_cps,
       read_cps: read_cps,
       write_one_cps: write_one_cps,
       read_one_cps: read_one_cps
     }
+
+    Map.merge(results, cpu_info)
   end
 
   defp time_fun2(times, fun, arg) do
diff --git a/lib/gpio/diagnostics/cpu.ex b/lib/gpio/diagnostics/cpu.ex
new file mode 100644
index 0000000..e3030f7
--- /dev/null
+++ b/lib/gpio/diagnostics/cpu.ex
@@ -0,0 +1,154 @@
+# SPDX-FileCopyrightText: 2024 Frank Hunleth
+#
+# SPDX-License-Identifier: Apache-2.0
+
+defmodule Circuits.GPIO.Diagnostics.CPU do
+  @moduledoc """
+  CPU
+  """
+
+  @doc """
+  Force the CPU to its slowest setting
+
+  This requires the Linux kernel to have the powersave CPU scaling governor available.
+  """
+  @spec force_slowest() :: :ok
+  def force_slowest() do
+    cpu_list()
+    |> Enum.each(&set_governor(&1, "powersave"))
+  end
+
+  @doc """
+  Force the CPU to its fastest setting
+
+  This requires the Linux kernel to have the performance CPU scaling governor available.
+  """
+  @spec force_fastest() :: :ok
+  def force_fastest() do
+    cpu_list()
+    |> Enum.each(&set_governor(&1, "performance"))
+  end
+
+  @doc """
+  Set the CPU to the specified frequency
+
+  This requires the Linux kernel to have the userspace CPU scaling governor available.
+  Not all frequencies are supported. The closest will be picked.
+  """
+  @spec set_frequency(number()) :: :ok
+  def set_frequency(frequency_mhz) do
+    cpus = cpu_list()
+    Enum.each(cpus, &set_governor(&1, "userspace"))
+    Enum.each(cpus, &set_frequency(&1, frequency_mhz))
+  end
+
+  defp set_governor(cpu, governor) do
+    File.write!("/sys/bus/cpu/devices/#{cpu}/cpufreq/scaling_governor", governor)
+  end
+
+  defp set_frequency(cpu, frequency_mhz) do
+    frequency_khz = round(frequency_mhz * 1000)
+    File.write!("/sys/bus/cpu/devices/#{cpu}/cpufreq/scaling_setspeed", to_string(frequency_khz))
+  end
+
+  @doc """
+  Return the string names for all CPUs
+
+  CPUs are named `"cpu0"`, `"cpu1"`, etc.
+  """
+  @spec cpu_list() :: [String.t()]
+  def cpu_list() do
+    case File.ls("/sys/bus/cpu/devices") do
+      {:ok, list} -> Enum.sort(list)
+      _ -> []
+    end
+  end
+
+  @doc """
+  Check benchmark suitability and return CPU information
+  """
+  @spec check_benchmark_suitability() :: %{
+          uname: String.t(),
+          cpu_count: non_neg_integer(),
+          speed_mhz: number(),
+          warnings?: boolean()
+        }
+  def check_benchmark_suitability() do
+    cpus = cpu_list()
+
+    scheduler_warnings? = Enum.all?(cpus, &check_cpu_scheduler/1)
+    {frequency_warnings?, mhz} = mean_cpu_frequency(cpus)
+
+    %{
+      uname: uname(),
+      cpu_count: length(cpus),
+      speed_mhz: mhz,
+      warnings?: scheduler_warnings? or frequency_warnings?
+    }
+  end
+
+  defp uname() do
+    case File.read("/proc/version") do
+      {:ok, s} -> String.trim(s)
+      {:error, _} -> "Unknown"
+    end
+  end
+
+  defp check_cpu_scheduler(cpu) do
+    case File.read("/sys/bus/cpu/devices/#{cpu}/cpufreq/scaling_governor") do
+      {:error, _} ->
+        io_warn("Could not check CPU frequency scaling for #{cpu}")
+        true
+
+      {:ok, text} ->
+        governor = String.trim(text)
+
+        if governor in ["powersave", "performance", "userspace"] do
+          false
+        else
+          io_warn(
+            "CPU #{cpu} is using a dynamic CPU frequency governor. Performance results may vary."
+          )
+
+          true
+        end
+    end
+  end
+
+  defp cpu_frequency_mhz(cpu) do
+    # Report the actual CPU frequency just in case something is throttling the governor (e.g., thermal throttling).
+    # The governor's target frequency is in the "scaling_cur_freq" file.
+    case File.read("/sys/bus/cpu/devices/#{cpu}/cpufreq/cpuinfo_cur_freq") do
+      {:ok, string} -> string |> String.trim() |> String.to_integer() |> Kernel./(1000)
+      {:error, _} -> 0.0
+    end
+  end
+
+  defp mean_cpu_frequency(cpu_list) do
+    speeds = cpu_list |> Enum.map(&cpu_frequency_mhz/1)
+
+    case speeds do
+      [] ->
+        {true, 0.0}
+
+      [speed] ->
+        {false, speed}
+
+      [first | _rest] ->
+        mean = Enum.sum(speeds) / length(speeds)
+
+        if abs(mean - first) < 0.001 do
+          {false, mean}
+        else
+          io_warn("CPU speeds don't all match: #{inspect(speeds)}")
+          {true, mean}
+        end
+    end
+  end
+
+  defp io_warn(text) do
+    [:yellow, "WARNING: ", text, :reset]
+    |> IO.ANSI.format()
+    |> IO.puts()
+  end
+end