Skip readonly CPU online files

Add warning and skip hotplugging (enabling/disabling) of a CPU if its
online file is unwritable/readonly. On some devices (e.g: Pixel 6)
CPU0 is often special and excluded from CPU hotplugging therefore
flag an appropriate warning but still allow benchmarks to run.

Test: ./scripts/benchmarks/benchmarks_run_target.sh --cpu big \
      --iterations 2 benchmarks/algorithm/DeltaBlue
Change-Id: I19d548f0df9d3d2d805f4bc1bdd787b3284603b7

1 files changed, 24 insertions, 16 deletions

diff --git a/devices/cpu_freq_utils.sh b/devices/cpu_freq_utils.sh
index 4794aded..0f005c51 100644
--- a/devices/cpu_freq_utils.sh
+++ b/devices/cpu_freq_utils.sh
@@ -76,25 +76,33 @@ set_state_cpus() {
       # Only raise an error if we were trying to disable CPU.
       if [[ $state -eq 0 ]]; then
         log E "Could not write to $online_file"
+        return 1
       fi
-    else
-      local new_state trial
+    fi
+
+    # Check that the online file is writable, if not skip it.
+    if [[ $(adb_shell "ls -l ${online_file} | grep -c 'w'") -eq 0 ]]; then
+      log W "CPU '${cpu}' is not writable"
+      continue
+    fi
+
+    # Try and set the CPU to the requested state.
+    local new_state trial
+    adb_shell "echo ${state} > $online_file"
+    new_state=$(safe adb_shell "cat $online_file")
+    for ((trial=1; trial <= max_trials && new_state != state; trial++)); do
+      # There might be a kthread hotplugging CPUs on and off (for example the
+      # thermal governor if the temperature is high), so let us wait for the
+      # device to cool down and retry.
+      log W "Failed to set CPU ${cpu} to state ${state}, retrying ${trial}..."
+      safe sleep 100s
       adb_shell "echo ${state} > $online_file"
       new_state=$(safe adb_shell "cat $online_file")
-      for ((trial=1; trial <= max_trials && new_state != state; trial++)); do
-        # There might be a kthread hotplugging CPUs on and off (for example the
-        # thermal governor if the temperature is high), so let us wait for the
-        # device to cool down and retry.
-        log W "Failed to set CPU ${cpu} to state ${state}, retrying ${trial}..."
-        safe sleep 100s
-        adb_shell "echo ${state} > $online_file"
-        new_state=$(safe adb_shell "cat $online_file")
-      done
-      # If after 10 trials there is still a failure, abort with an error.
-      if [[ "${new_state}" != "${state}" ]]; then
-        log E "Failed to set CPU ${cpu} to state ${state}, after ${trial} trials"
-        return 1
-      fi
+    done
+    # If after 10 trials there is still a failure, abort with an error.
+    if [[ "${new_state}" != "${state}" ]]; then
+      log E "Failed to set CPU ${cpu} to state ${state}, after ${trial} trials"
+      return 1
     fi
 
     log I "Successfully set CPU ${cpu} to state ${state}"