[PATCH] drm/amdgpu: Add sysfs file for VBIOS

[Felix Kuehling]

On 2017-08-25 03:40 PM, Deucher, Alexander wrote:
>> -----Original Message-----
>> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On Behalf
>> Of Felix Kuehling
>> Sent: Friday, August 25, 2017 3:34 PM
>> To: amd-gfx at lists.freedesktop.org
>> Subject: Re: [PATCH] drm/amdgpu: Add sysfs file for VBIOS
>>
>> I think the power measurement is a bit of a hack right now. It requires
>> pinging the SMU twice to start and stop the measurement, and waiting for
>> some time (but not too long) in between. I think if we want to expose
>> this via hwmon, we'll need to have some kind of timer that polls it in
>> regular intervals in the background and updates a value that can be
>> queried through HWMon without delay.
> I don't know that hwmon has any requirements with respect to delay.  I think a slight delay in reading it back through hwmon is preferable to a background thread polling it. Regular polling may also have negative impacts on performance or stability, depending on how it was validated.

If an application is reading hwmon data from 4 GPUs and each query for
power usage from each GPU takes one second, that would seriously limit
the update frequency of the application.

Maybe the first read could block long enough to get useful data. But
subsequent reads could probably avoid blocking if we keep track of the
time stamp of the last query. If it was very recently, we can return the
last value. If it was long enough ago, we can get an updated value from
the SMU. If the last query was too long ago, we start over and block for
a second.

Regards,
  Felix

> Alex
>
>> Regards,
>>   Felix
>>
>>
>> On 2017-08-25 11:56 AM, Deucher, Alexander wrote:
>>>> -----Original Message-----
>>>> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On
>> Behalf
>>>> Of Russell, Kent
>>>> Sent: Friday, August 25, 2017 9:00 AM
>>>> To: StDenis, Tom; Christian König; amd-gfx at lists.freedesktop.org
>>>> Subject: RE: [PATCH] drm/amdgpu: Add sysfs file for VBIOS
>>>>
>>>> There is GPU Power usage reported through amdgpu_pm_info, which
>> also
>>>> has some other information as well. I'd like that in sysfs, but I am unsure if
>>>> we are  allowed to due to the other information reported there.
>>> For power and voltage, I believe there are standard hwmon interfaces.  It
>> would probably be best to expose it via those.  For clocks/pcie, I think you
>> can already determine them via the existing pp sysfs interfaces.
>>> Alex
>>>
>>>>  Kent
>>>>
>>>> -----Original Message-----
>>>> From: StDenis, Tom
>>>> Sent: Friday, August 25, 2017 8:58 AM
>>>> To: Christian König; Russell, Kent; amd-gfx at lists.freedesktop.org
>>>> Subject: Re: [PATCH] drm/amdgpu: Add sysfs file for VBIOS
>>>>
>>>> On 25/08/17 08:56 AM, Christian König wrote:
>>>>> Hi Kent,
>>>>>
>>>>> agree on the VBIOS dump file, that clearly belongs to debugsf.
>>>>>
>>>>> The power usage stuff I can't say much about cause I'm not deeply into
>>>>> this, but keep in mind the restriction for sysfs:
>>>>> 1. It's a stable interface. So it must be very well designed.
>>>>> 2. Only one value per file. I think the power stuff doesn't fulfill
>>>>> that requirement at the moment.
>>>> What "power" stuff are we talking about?  The sensors interface or the
>>>> pm_info or something else?
>>>>
>>>> Keep in mind umr uses the sensors debugfs file in --top mode.
>>>>
>>>> Tom
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