Date:   Thu, 13 Apr 2023 03:27:37 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org,
        Emil Velikov <emil.l.velikov@...il.com>,
        Christopher Healy <healych@...zon.com>,
        open list <linux-kernel@...r.kernel.org>,
        Sean Paul <sean@...rly.run>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        freedreno@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH v2 0/2] drm: fdinfo memory stats

On 12/04/2023 23:34, Rob Clark wrote:
> On Wed, Apr 12, 2023 at 1:19 PM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
>>
>> On Wed, 12 Apr 2023 at 23:09, Rob Clark <robdclark@...il.com> wrote:
>>>
>>> On Wed, Apr 12, 2023 at 5:47 AM Rodrigo Vivi <rodrigo.vivi@...el.com> wrote:
>>>>
>>>> On Wed, Apr 12, 2023 at 10:11:32AM +0200, Daniel Vetter wrote:
>>>>> On Wed, Apr 12, 2023 at 01:36:52AM +0300, Dmitry Baryshkov wrote:
>>>>>> On 11/04/2023 21:28, Rob Clark wrote:
>>>>>>> On Tue, Apr 11, 2023 at 10:36 AM Dmitry Baryshkov
>>>>>>> <dmitry.baryshkov@...aro.org> wrote:
>>>>>>>>
>>>>>>>> On Tue, 11 Apr 2023 at 20:13, Rob Clark <robdclark@...il.com> wrote:
>>>>>>>>>
>>>>>>>>> On Tue, Apr 11, 2023 at 9:53 AM Daniel Vetter <daniel@...ll.ch> wrote:
>>>>>>>>>>
>>>>>>>>>> On Tue, Apr 11, 2023 at 09:47:32AM -0700, Rob Clark wrote:
>>>>>>>>>>> On Mon, Apr 10, 2023 at 2:06 PM Rob Clark <robdclark@...il.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> From: Rob Clark <robdclark@...omium.org>
>>>>>>>>>>>>
>>>>>>>>>>>> Similar motivation to other similar recent attempt[1].  But with an
>>>>>>>>>>>> attempt to have some shared code for this.  As well as documentation.
>>>>>>>>>>>>
>>>>>>>>>>>> It is probably a bit UMA-centric, I guess devices with VRAM might want
>>>>>>>>>>>> some placement stats as well.  But this seems like a reasonable start.
>>>>>>>>>>>>
>>>>>>>>>>>> Basic gputop support: https://patchwork.freedesktop.org/series/116236/
>>>>>>>>>>>> And already nvtop support: https://github.com/Syllo/nvtop/pull/204
>>>>>>>>>>>
>>>>>>>>>>> On a related topic, I'm wondering if it would make sense to report
>>>>>>>>>>> some more global things (temp, freq, etc) via fdinfo?  Some of this,
>>>>>>>>>>> tools like nvtop could get by trawling sysfs or other driver specific
>>>>>>>>>>> ways.  But maybe it makes sense to have these sort of things reported
>>>>>>>>>>> in a standardized way (even though they aren't really per-drm_file)
>>>>>>>>>>
>>>>>>>>>> I think that's a bit much layering violation, we'd essentially have to
>>>>>>>>>> reinvent the hwmon sysfs uapi in fdinfo. Not really a business I want to
>>>>>>>>>> be in :-)
>>>>>>>>>
>>>>>>>>> I guess this is true for temp (where there are thermal zones with
>>>>>>>>> potentially multiple temp sensors.. but I'm still digging my way thru
>>>>>>>>> the thermal_cooling_device stuff)
>>>>>>>>
>>>>>>>> It is slightly ugly. All thermal zones and cooling devices are virtual
>>>>>>>> devices (so, even no connection to the particular tsens device). One
>>>>>>>> can either enumerate them by checking
>>>>>>>> /sys/class/thermal/thermal_zoneN/type or enumerate them through
>>>>>>>> /sys/class/hwmon. For cooling devices again the only enumeration is
>>>>>>>> through /sys/class/thermal/cooling_deviceN/type.
>>>>>>>>
>>>>>>>> Probably it should be possible to push cooling devices and thermal
>>>>>>>> zones under corresponding providers. However I do not know if there is
>>>>>>>> a good way to correlate cooling device (ideally a part of GPU) to the
>>>>>>>> thermal_zone (which in our case is provided by tsens / temp_alarm
>>>>>>>> rather than GPU itself).
>>>>>>>>
>>>>>>>>>
>>>>>>>>> But what about freq?  I think, esp for cases where some "fw thing" is
>>>>>>>>> controlling the freq we end up needing to use gpu counters to measure
>>>>>>>>> the freq.
>>>>>>>>
>>>>>>>> For the freq it is slightly easier: /sys/class/devfreq/*, devices are
>>>>>>>> registered under proper parent (IOW, GPU). So one can read
>>>>>>>> /sys/class/devfreq/3d00000.gpu/cur_freq or
>>>>>>>> /sys/bus/platform/devices/3d00000.gpu/devfreq/3d00000.gpu/cur_freq.
>>>>>>>>
>>>>>>>> However because of the components usage, there is no link from
>>>>>>>> /sys/class/drm/card0
>>>>>>>> (/sys/devices/platform/soc@...e00000.display-subsystem/ae01000.display-controller/drm/card0)
>>>>>>>> to /sys/devices/platform/soc@...d00000.gpu, the GPU unit.
>>>>>>>>
>>>>>>>> Getting all these items together in a platform-independent way would
>>>>>>>> be definitely an important but complex topic.
>>>>>>>
>>>>>>> But I don't believe any of the pci gpu's use devfreq ;-)
>>>>>>>
>>>>>>> And also, you can't expect the CPU to actually know the freq when fw
>>>>>>> is the one controlling freq.  We can, currently, have a reasonable
>>>>>>> approximation from devfreq but that stops if IFPC is implemented.  And
>>>>>>> other GPUs have even less direct control.  So freq is a thing that I
>>>>>>> don't think we should try to get from "common frameworks"
>>>>>>
>>>>>> I think it might be useful to add another passive devfreq governor type for
>>>>>> external frequencies. This way we can use the same interface to export
>>>>>> non-CPU-controlled frequencies.
>>>>>
>>>>> Yeah this sounds like a decent idea to me too. It might also solve the fun
>>>>> of various pci devices having very non-standard freq controls in sysfs
>>>>> (looking at least at i915 here ...)
>>>>
>>>> I also like the idea of having some common infrastructure for the GPU freq.
>>>>
>>>> hwmon have a good infrastructure, but they are more focused on individual
>>>> monitoring devices and not very welcomed to embedded monitoring and control.
>>>> I still want to check the opportunity to see if at least some freq control
>>>> could be aligned there.
>>>>
>>>> Another thing that complicates that is that there are multiple frequency
>>>> domains and controls with multipliers in Intel GPU that are not very
>>>> standard or easy to integrate.
>>>>
>>>> On a quick glace this devfreq seems neat because it aligns with the cpufreq
>>>> and governors. But again it would be hard to align with the multiple domains
>>>> and controls. But it deserves a look.
>>>>
>>>> I will take a look to both fronts for Xe: hwmon and devfreq. Right now on
>>>> Xe we have a lot less controls than i915, but I can imagine soon there
>>>> will be requirements to make that to grow and I fear that we end up just
>>>> like i915. So I will take a look before that happens.
>>>
>>> So it looks like i915 (dgpu only) and nouveau already use hwmon.. so
>>> maybe this is a good way to expose temp.  Maybe we can wire up some
>>> sort of helper for drivers which use thermal_cooling_device (which can
>>> be composed of multiple sensors) to give back an aggregate temp for
>>> hwmon to report?
>>
>> The thermal_device already registers the hwmon, see below. The
>> question is about linking that hwmon to the drm. Strictly speaking, I
>> don't think that we can reexport it in a clean way.
>>
>> # grep gpu /sys/class/hwmon/hwmon*/name
>> /sys/class/hwmon/hwmon15/name:gpu_top_thermal
>> /sys/class/hwmon/hwmon24/name:gpu_bottom_thermal
> 
> I can't get excited about userspace relying on naming conventions or
> other heuristics like this.  

As you can guess, me neither. We are not in 2.4 world anymore.

> Also, userspace's view of the world is
> very much that there is a "gpu card", not a collection of parts.
> (Windows seems to have the same view of the world.)  So we have the
> component framework to assemble the various parts together into the
> "device" that userspace expects to deal with.  We need to do something
> similar for exposing temp and freq.

I think we are lookin for something close to device links. We need to 
create a userspace-visible link from one device to another across device 
hierarchy. Current device_link API is tied to suspend/resume, but the 
overall idea seems to be close enough (in my opinion).

> 
>> # ls /sys/class/hwmon/hwmon15/ -l
>> lrwxrwxrwx    1 root     root             0 Jan 26 08:14 device ->
>> ../../thermal_zone15
>> -r--r--r--    1 root     root          4096 Jan 26 08:14 name
>> drwxr-xr-x    2 root     root             0 Jan 26 08:15 power
>> lrwxrwxrwx    1 root     root             0 Jan 26 08:12 subsystem ->
>> ../../../../../class/hwmon
>> -r--r--r--    1 root     root          4096 Jan 26 08:14 temp1_input
>> -rw-r--r--    1 root     root          4096 Jan 26 08:12 uevent
>>
>>> Freq could possibly be added to hwmon (ie. seems like a reasonable
>>> attribute to add).  Devfreq might also be an option but on arm it
>>> isn't necessarily associated with the drm device, whereas we could
>>> associate the hwmon with the drm device to make it easier for
>>> userspace to find.
>>
>> Possibly we can register a virtual 'passive' devfreq being driven by
>> another active devfreq device.
> 
> That's all fine and good, but it has the same problem that existing
> hwmon's associated with the cooling-device have..
> 
> BR,
> -R
> 
>>>
>>> BR,
>>> -R
>>>
>>>>>
>>>>> I guess it would minimally be a good idea if we could document this, or
>>>>> maybe have a reference implementation in nvtop or whatever the cool thing
>>>>> is rn.
>>>>> -Daniel
>>>>>
>>>>>>
>>>>>>>
>>>>>>> BR,
>>>>>>> -R
>>>>>>>
>>>>>>>>>
>>>>>>>>>> What might be needed is better glue to go from the fd or fdinfo to the
>>>>>>>>>> right hw device and then crawl around the hwmon in sysfs automatically. I
>>>>>>>>>> would not be surprised at all if we really suck on this, probably more
>>>>>>>>>> likely on SoC than pci gpus where at least everything should be under the
>>>>>>>>>> main pci sysfs device.
>>>>>>>>>
>>>>>>>>> yeah, I *think* userspace would have to look at /proc/device-tree to
>>>>>>>>> find the cooling device(s) associated with the gpu.. at least I don't
>>>>>>>>> see a straightforward way to figure it out just for sysfs
>>>>>>>>>
>>>>>>>>> BR,
>>>>>>>>> -R
>>>>>>>>>
>>>>>>>>>> -Daniel
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> BR,
>>>>>>>>>>> -R
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>> [1] https://patchwork.freedesktop.org/series/112397/
>>>>>>>>>>>>
>>>>>>>>>>>> Rob Clark (2):
>>>>>>>>>>>>     drm: Add fdinfo memory stats
>>>>>>>>>>>>     drm/msm: Add memory stats to fdinfo
>>>>>>>>>>>>
>>>>>>>>>>>>    Documentation/gpu/drm-usage-stats.rst | 21 +++++++
>>>>>>>>>>>>    drivers/gpu/drm/drm_file.c            | 79 +++++++++++++++++++++++++++
>>>>>>>>>>>>    drivers/gpu/drm/msm/msm_drv.c         | 25 ++++++++-
>>>>>>>>>>>>    drivers/gpu/drm/msm/msm_gpu.c         |  2 -
>>>>>>>>>>>>    include/drm/drm_file.h                | 10 ++++
>>>>>>>>>>>>    5 files changed, 134 insertions(+), 3 deletions(-)
>>>>>>>>>>>>
>>>>>>>>>>>> --
>>>>>>>>>>>> 2.39.2
>>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>>> Daniel Vetter
>>>>>>>>>> Software Engineer, Intel Corporation
>>>>>>>>>> http://blog.ffwll.ch
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> With best wishes
>>>>>>>> Dmitry
>>>>>>
>>>>>> --
>>>>>> With best wishes
>>>>>> Dmitry
>>>>>>
>>>>>
>>>>> --
>>>>> Daniel Vetter
>>>>> Software Engineer, Intel Corporation
>>>>> http://blog.ffwll.ch
>>
>>
>>
>> --
>> With best wishes
>> Dmitry

-- 
With best wishes
Dmitry

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