Re: Supporting Intel GPU tracing in gpuvis

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On 11/20/2017 06:01 AM, Tvrtko Ursulin wrote:

Hi,

On 16/11/2017 20:42, Michael Sartain wrote:
On Wed, Sep 6, 2017, at 02:09 AM, Chris Wilson wrote:
Quoting Daniel Vetter (2017-09-06 08:46:50)
Hi Pierre,

On Tue, Sep 5, 2017 at 11:15 PM, Pierre-Loup A. Griffais
<pgriffais@xxxxxxxxxxxxxxxxx> wrote:
Hi Daniel,

In the past couple of months we've been working on gpuvis, a GPU tracing tool similar to GPUView on Windows. It's lower level than other API-based tracing tools and lets you debug system-wide GPU scheduling issues, eg.
interaction between several processes using the GPU, which is pretty
critical for VR usecases.

It's all based on ftrace; we've initially developped it with support for amdgpu, and had to patch the kernel code there to change what tracing events are reported and how. Now that we have a good idea of what's needed and it's more or less proven in production, we were wondering if you had any interest in adding a similar set of events for Intel GPUs so we could read them and present them the same way? We have pretty specific requirements, but this work-in-progress documentation should give a good idea of what they are:

https://github.com/mikesart/gpuvis/wiki/Overview

We already have those tracepoint equivs and a script to generate a
similar visualisation: intel-gpu-tools/scripts/trace.pl, but only
looking at the scheduling issue from the gpu pov. But it's really only a
dev toy atm, plugging the gap between userspace and the gpu has been on
the perennial wishlist.
-Chris

I added Intel event visualization to gpuvis based on your trace.pl
script. Screenshot at the top of the wiki page here:

https://github.com/mikesart/gpuvis/wiki/TechDocs-Intel

In that screenshot the mouse is hovering over the ctx=30,seqno=1900 bar
which selects those events in the event list and shows a tooltip with
the submit, execute, etc info.

It certainly looks immensely better than my browser based hack. But unfortunately I still did not get round actually trying your tool.

How scalable it is - meaning - can it handle very busy and huge traces?

The typical SteamVR trace in our "DVR" plumbing (always tracing in the background) has about 500k events over ~20 seconds. I can zoom and scrub through it at 60fps without issues here.


Is there any outlook of it getting packaged in some distro?

The tool itself is standalone and very easy to package; Mike recently wrote some plumbing example scripts around it that can get useful captures, so I would think we're in better shape for packaging now than before they existed. We bundle it with SteamVR so haven't really spent any time looking into packaging.


For the amdgpu driver, we're able to get the submit information from
user space and associate those events to specific processes. Example of
that is here:

https://github.com/mikesart/gpuvis/wiki/TechDocs-AMDGpu

If you ever get a chance to try gpuvis and have any feedback, we'd love
to hear it.  Also if you ever get userspace tracepoint data in, let me
know and I'd be happy to hook that up as well.

What kind of information is missing to wire up this missing bit? I mean the thing you are referring to as user space submit data, what is that?

The main thing is to be able to associate a chunk of GPU work with a userspace process. Currently, there's no tracepoint we're aware of in the work submission ioctl, which means that while the GPU tasks are properly displayed, they're anonymous. The main intent behind gpuvis is to be able to debug multi-process GPU interaction and timing problems, so having a tracepoint in the submit ioctl lets us associate the user context of the application that submitted the work with the work itself if it shares the same identifying seqnos/ids. gpuvis can then show you thread information about that process, color-code for easy disambiguation, etc.


Btw one new thing we are close to merging to i915 is the perf PMU support. That will enable real-time monitoring of per-engine busyness, waits, frequency, power, maybe more in the future like queue-depth. I don't know if things like that would be interesting for gpuvis? Some of it can be inferred from the tracepoints already in post-processing so there is some overlap. I am not sure, but thought to mention it. This is the series: https://patchwork.freedesktop.org/series/27488/. It is used via existing perf userspace API.

Seems like the kind of thing gpuvis could happily overlay on top of the trace with its plotting functionality.


Regards,

Tvrtko


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