ci: Lock Intel GPU frequency for performance tests

In order to ensure consistent results when running performance tests,
lock the frequency for Intel GPUs to ~70% of the maximum allowed by
hardware.

This seems to offer a good balance between execution speed and results
consistency.

An increase of the frequency will also increase the rate of throttling
events, with a negative impact on consistency. Such events are logged,
as in the following example:

  GPU throttling detected: act=200 min=850 cur=850 RPn=100

This shows the actual GPU frequency (200 MHz) dropped below the minimum
requested (850 MHz).

For more details about the various frequency information sources, please
see the script header comments in ".gitlab-ci/common/intel-gpu-freq.sh".

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Acked-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15662>

.gitlab-ci/common/init-stage2.sh

@@ -60,6 +60,10 @@ if [ "$HWCI_FREQ_MAX" = "true" ]; then
   # Disable GPU runtime power management
   GPU_AUTOSUSPEND=`find /sys/devices -name autosuspend_delay_ms | grep gpu | head -1`
   test -z "$GPU_AUTOSUSPEND" || echo -1 > $GPU_AUTOSUSPEND || true
+
+  # Lock Intel GPU frequency to 70% of the maximum allowed by hardware
+  # and enable throttling detection & reporting.
+  ./intel-gpu-freq.sh -s 70% -g all -d
 fi
 
 # Increase freedreno hangcheck timer because it's right at the edge of the