[Nouveau] Addressing the problem of noisy GPUs under Nouveau

[Martin Peres]

Hey,

Thanks for your answer, Andy!

On 22/11/17 04:06, Ilia Mirkin wrote:
> On Tue, Nov 21, 2017 at 8:29 PM, Andy Ritger <aritger at nvidia.com> wrote:
>> Hi Martin,
> 
> Martin should have complete answers,
> 
>>
>> I was asked to clarify a few things:
>>
>> (1) Are all the user reports of loud fans on Fermi-era GPUs?
> 
> Yes. Although I believe some GK208 users are also having trouble,
> including yours truly. (It's been quite a while since I've checked
> though... my memory is weak in that regard.)

We did not hear back from a lot of users about these issues, but I can
see that most GF108 vbios in our vbios repo are problematic, and some
GK106/GT215/GT216/GT218 might be too.

> 
>>
>> (2) When the VBIOS POSTs the card, it loads initial ucode onto the Falcon
>> processor (PMU), which will do basic fan management on its own.  We call this
>> init ucode "IFR" (Init From ROM).  nvidia.ko will restore the IFR ucode when
>> unloaded.  I assume the loud fan symptom occurs after Nouveau is loaded and
>> running, correct?  I.e., this is a problem in Nouveau's fan control
>> programming, rather than a problem in IFR.
> 
> Correct.

Indeed.

> 
>>
>> (3) IFR will run until something else is loaded on the Falcon processor (PMU).
>> On Fermi, I assume the Nouveau kernel driver is uploading the Nouveau-written
>> ucode from here:
>>
>>     drivers/gpu/drm/nouveau/nvkm/subdev/pmu/fuc
>>
>> correct?  I only ask to rule out the possibility that IFR and Nouveau are both
>> attempting to program fans simultaneously.  The symptoms you describe don't
>> sound like that, but just double checking...
> 
> Correct.

Indeed.

> 
>>
>> (4) Given the PMU ucode debacle, I'm embarrassed to ask, but at least on Fermi,
>> how much does Nouveau strictly depend on Nouveau's PMU ucode?  Would it be an
>> option to just let IFR continue to manage fans?
> 
> Reclocking is still on our horizon, which clearly won't happen without
> nouveau PMU code loaded. Not sure what it's used for until reclocking
> becomes a thing on Fermi.

Yeah, this would hinder our reclocking efforts :s

The best idea I can come up with is to fake the temperature (register
0x20408) to 1°C (minimum the hardware allows us) and read the PWM duty,
then we can get the maximum duty by setting the temperature to the
fan_boost threshold.

Not sure we have a sure-way of computing the fan_boost threshold though,
maybe we can just use of the thermal throttling threshold for this (more
on this later in the email).

In any case, all of these solutions are workarounds. Given that the code
to compute these values is already found in vbioses, why is it a problem
to share the meaning of all the values in the fan calibration table,
and/or the algorithm?

> 
>>
>> (5) Lastly, I was asked how Nouveau determines what fan speed to (attempt
>> to) program.

Oh, thanks for giving me an idea about what the other values in this
table may be about :D

Anyways, the current code uses the entry id 0x46 of the thermal table
(bit P, offset 0x10) to find out what are the thermal points for
$fan_min and $fan_max. The $fan_min and $fan_max values are found in the
entry id 0x22 of the same table.

If the 0x46 entry is not present in the thermal table (which seems to be
the norm for Fermi), we revert to default values: 40 -> 85°C.

With these 4 values, we get 2 trip points (temp_min, fan_min)
and(temp_max, fan_max), and we merely do linear interpolation between them.

> 
> I'll let Martin answer this, but as you're probably aware, there's 2
> different ways this can be done - there might be a PWM, we might have
> to toggle it manually. Maybe something else still.

The manual toggle fans are only present on pre-tesla GPUs, let's ignore
them here, because we know what to do there.

All recent (2006+) GPUs use PWM, and anything after the GT215 use this
fan calibration table which took me a while to find, and that is still
mostly a mystery to me :s

> 
> Have a look at drm/nouveau/nvkm/subdev/therm/fan.c and the various
> bits it ends up calling (pre-GF119 fermi's end up with the nv50
> fan_set, I believe).
> 
> The bios stuff is parsed in nvkm/subdev/bios/fan.c and therm.c,
> although I believe Martin's latest analysis is more advanced than
> what's in that code.

Absolutely :) I have not updated Nouveau yet, in fear of setting a value
lower than what the proprietary driver does...

> 
> Martin's question was very long, but it boils down to this:
> 
> How do we compute the correct values to write into the e114/e118 pwm
> registers based on the VBIOS contents and current state of the board
> (like temperature).

Unfortunately, it can also be the e11c/e120 couple, or 0x200d8/dc on
GF119+, or 0x200cd/d0 on Kepler+.

At least, it looks like we know which PWM controler we need to drive, so
I did not want to muddy the water even more by giving register
addresses, rather concentrating on the problem at hand: How to compute
the duty value for the PWM controler.

> 
> We generally do this right, but appear to get it extra-wrong for certain GPUs.

Yes... So far, we are always safe, but users tend to mind when their
computer sound like a jumbo jet at take off... Who would have thought? :D

Anyway, looking forward to your answer!

Cheers,
Martin