On 7/3/2023 3:20 PM, Dmitry Baryshkov wrote:
On Tue, 4 Jul 2023 at 00:40, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
On 6/19/2023 5:08 PM, Dmitry Baryshkov wrote:
DPU performance module contains code to change performance state
calculations. In addition to normal (sum plane and CRTC requirements),
it can work in 'minimal' or 'fixed' modes. Both modes are impractical,
since they can easily end up with the display underruns. Userspace also
should not depend on these modes availability, since they are tuned
through debugfs, which might not be available.
Drop relevant code to simplify performance state calculations.
Suggested-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
---
Sorry but NAK on this change for two reasons:
This mode is not for usermode to depend on but for debugging. I have
personally used both the perf max and perf min modes for debug.
1) The purpose is that, if you do see an underrun, you can force the
perf mode as it will select max clk and bw rate
So something like below:
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 2 > perf_mode
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 300000000 >
fix_core_clk_rate
This will allow us to force the clk to a particular value to see at what
point it starts underruning
Also you can even do
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 1 > perf_mode
This will automatically max out the clk and BW
With this, you can figure out if underrun is a performance related
underrun or a misconfiguration. We used it even recently to debug the
performance issue with pclk reduction
Hmm, 1 is minimum, not maxumum.
The name is kind of confusing.
Yes 1 is min perf mode but it maxes out the clocks and BW.
I guess its named that way because a min perf mode gives you the minimum
savings in terms of power.
2) Sometimes, you even want to force an underrun to debug devcoredump OR
the recovery code. Forcing the min clk mode by doing
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 19200000 >
fix_core_clk_rate
localhost /sys/kernel/debug/dri/1/debug/core_perf # echo 2 > perf_mode
Is the easiest way to trigger the recovery handler.
Hence I am not at all convinced of dropping this.
I see, thanks for sharing the usecases. However I still think that it
is overcomplicated for the debugging feature. What about dropping all
perf modes and providing just 'override_core_clk_rate' and
'override_avg_bw', 'override_peak_bw'?
No, we need both. Let me explain why:
1) Having just the min perf mode, directly uses the max clk and bw. This
is useful when you just want to run at the max and see the behavior
2) If you want to figure out what is the sweet spot where the issue does
not happen you need the "fixed" mode to find the range where the issue
doesnt happen
This is one of the oldest and most effective debugging mechanisms.
I dont want to touch this and I personally use this quite often.
