[Bug 72385] [HSW] GPU peak frequency can't reach peak immediately as exceptedly

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https://bugs.freedesktop.org/show_bug.cgi?id=72385

--- Comment #5 from ZhaoShengyan <shengyanx.zhao at intel.com> ---
Daniel Vetter & Chris Wilson , we tried with kernel
3.13.0-rc1_drm-intel-nightly_41199e_20131207+ with the following two
experiments:
1. Experiment One:
1> Made a script to cat /sys/class/drm/card0/gt_cur_freq_mhz every second and
name the script as ls_cur_freq_mhz.sh, you can refer to the following details:
#file: ls_cur_freq_mhz.sh
#!/bin/bash
peak_freq=$(cat /sys/class/drm/card0/gt_max_freq_mhz)
min_freq=$(cat /sys/class/drm/card0/gt_min_freq_mhz)
echo "freq_rangle: [${min_freq}~${peak_freq}]MHz"
while true
do
    cur_freq=$(cat /sys/class/drm/card0/gt_cur_freq_mhz)
    echo "current frequency is: ${cur_freq}"
    sleep 1
done

2> . ls_cur_freq_mhz.sh in one terminal;
3> Startup glxgears & in another terminal;
4> check the current frequency output, if got current frequency is 200, just
repeat 3>, until got frequency is 1100.
4> pkill glxgears and moniter the current frequency output.

In kernel 3.13.0-rc1_drm-intel-nightly_41199e_20131207+, we tried more than 20
times, generally, run 2 glxgears at background will lead to current frequency
to 1100MHz. Then, we pkill glxgears and moniter the current frequency output.
The frequency falling down immediately just corresponding we kill the glxgears
process.
In kernel kernel-3.12.2_20131203+-2.x86_64, we found more than 2 glxgears can
also trigger to peak frequency, but after we kill all the glxgears via pkill,
the current frequency output still just fall down by 100(from 1100 to 1000). 

2. Experiment Two:
Still use script ls_cur_freq_mhz.sh to moniter the current frequency output.
However, we changed a heavy-load game with fullscreen mode. Accordingly, we
discover kernel 3.13.0-rc1_drm-intel-nightly_41199e_20131207+ can reach to peak
frequency 1100, and can fall down to 200 as soon as the game process exit.
However, when we changed kernel to kernel-3.12.2_20131203+-2.x86_64, the
frequency output changed from 300 to 1100, and when the game process exit the
current frequency keep at 550. this will no change though there is no workload
running.  





(In reply to comment #3)
> They also have an issue with the freq not going down quickly afterwards, imo
> that's worth testing a bit ...

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