On 13/02/2021 04:20, Rob Clark wrote:
On Fri, Feb 12, 2021 at 5:56 PM Lionel Landwerlin <lionel.g.landwer...@intel.com> wrote:On 13/02/2021 03:38, Rob Clark wrote:On Fri, Feb 12, 2021 at 5:08 PM Lionel Landwerlin <lionel.g.landwer...@intel.com> wrote:We're kind of in the same boat for Intel.Access to GPU perf counters is exclusive to a single process if you want to build a timeline of the work (because preemption etc...).ugg, does that mean extensions like AMD_performance_monitor doesn't actually work on intel?It work,s but only a single app can use it at a time.I see.. on the freedreno side we haven't really gone down the preemption route yet, but we have a way to hook in some safe/restore cmdstream
That's why I think, for Intel HW, something like gfx-pps is probably best to pull out all the data on a timeline for the entire system.
Then the drivers could just provide timestamp on the timeline to annotate it.
-Lionel
The best information we could add from mesa would a timestamp of when a particular drawcall started. But that's pretty much when timestamps queries are. Were you thinking of particular GPU generated data you don't get from gfx-pps?>From the looks of it, currently I don't get *any* GPU generated data from gfx-pps ;-)Maybe file a bug? : https://gitlab.freedesktop.org/Fahien/gfx-pps/-/blob/master/src/gpu/intel/intel_driver.ccWe can ofc sample counters from a separate process as well... I have a curses tool (fdperf) which does this.. but running outside of gpu cmdstream plus counters losing context across suspend/resume makes it less than perfect.Our counters are global so to give per application values, we need to post process a stream of HW counter snapshots.And something that works the same way as AMD_performance_monitor under the hook gives a more precise look at which shaders (for ex) are consuming the most cycles.In our implementation that precision (in particular when a drawcall ends) comes at a stalling cost unfortunately.yeah, stalling on our end too for per-draw counter snapshots.. but if you are looking for which shaders to optimize that doesn't matter *that* much.. they'll be some overhead, but it's not really going to change which draws/shaders are expensive.. just mean that you lose out on pipelining of the state changes BR, -RFor cases where we can profile a trace, frameretrace and related tools is pretty great.. but it would be nice to have similar visibility for actual games (which for me, mostly means android games, since so far no aarch64 steam store), but also give game developers good tools (or at least the same tools that they get with other closed src drivers on android).Sure, but frame analysis is different than live monitoring of the system. On Intel's HW you don't get the same level of details in both cases, and apart for a few timestamps, I think gfx-pps is as good as you gonna get for live stuff. -LionelBR, -RThanks, -Lionel On 13/02/2021 00:12, Alyssa Rosenzweig wrote:My 2c for Mali/Panfrost -- For us, capturing GPU perf counters is orthogonal to rendering. It's expected (e.g. with Arm's tools) to do this from a separate process. Neither Mesa nor the DDK should require custom instrumentation for the low-level data. Fahien's gfx-pps handles this correctly for Panfrost + Perfetto as it is. So for us I don't see the value in modifying Mesa for tracing. On Fri, Feb 12, 2021 at 01:34:51PM -0800, John Bates wrote:(responding from correct address this time) On Fri, Feb 12, 2021 at 12:03 PM Mark Janes <mark.a.ja...@intel.com> wrote:I've recently been using GPUVis to look at trace events. On Intel platforms, GPUVis incorporates ftrace events from the i915 driver, performance metrics from igt-gpu-tools, and userspace ftrace markers that I locally hack up in Mesa.GPUVis is great. I would love to see that data combined with userspace events without any need for local hacks. Perfetto provides on-demand trace events with lower overhead compared to ftrace, so for example it is acceptable to have production trace instrumentation that can be captured without dev builds. To do that with ftrace it may require a way to enable and disable the ftrace file writes to avoid the overhead when tracing is not in use. This is what Android does with systrace/atrace, for example, it uses Binder to notify processes about trace sessions. Perfetto does that in a more portable way.It is very easy to compile the GPUVis UI. Userspace instrumentation requires a single C/C++ header. You don't have to access an external web service to analyze trace data (a big no-no for devs working on preproduction hardware). Is it possible to build and run the Perfetto UI locally?Yes, local UI builds are possible <https://github.com/google/perfetto/blob/5ff758df67da94d17734c2e70eb6738c4902953e/ui/README.md>. Also confirmed with the perfetto team <https://discord.gg/35ShE3A> that trace data is not uploaded unless you use the 'share' feature.Can it display arbitrary trace events that are written to /sys/kernel/tracing/trace_marker ?Yes, I believe it does support that via linux.ftrace data source <https://perfetto.dev/docs/quickstart/linux-tracing>. We use that for example to overlay CPU sched data to show what process is on each core throughout the timeline. There are many ftrace event types <https://github.com/google/perfetto/tree/5ff758df67da94d17734c2e70eb6738c4902953e/protos/perfetto/trace/ftrace> in the perfetto protos.Can it be extended to show i915 and i915-perf-recorder events?It can be extended to consume custom data sources. One way this is done is via a bridge daemon, such as traced_probes which is responsible for capturing data from ftrace and /proc during a trace session and sending it to traced. traced is the main perfetto tracing daemon that notifies all trace data sources to start/stop tracing and communicates with user tracing requests via the 'perfetto' command.John Bates <jba...@chromium.org> writes:I recently opened issue 4262 <https://gitlab.freedesktop.org/mesa/mesa/-/issues/4262> to begin the discussion on integrating perfetto into mesa. *Background* System-wide tracing is an invaluable tool for developers to find and fix performance problems. The perfetto project enables a combined view oftracedata from kernel ftrace, GPU driver and various manually-instrumented tracepoints throughout the application and system. This helps developers quickly answer questions like: - How long are frames taking? - What caused a particular frame drop? - Is it CPU bound or GPU bound? - Did a CPU core frequency drop cause something to go slower thanusual?- Is something else running that is stealing CPU or GPU time? Could I fix that with better thread/context priorities? - Are all CPU cores being used effectively? Do I needsched_setaffinityto keep my thread on a big or little core? - What’s the latency between CPU frame submit and GPU start? *What Does Mesa + Perfetto Provide?* Mesa is in a unique position to produce GPU trace data for several GPU vendors without requiring the developer to build and install additional tools like gfx-pps <https://gitlab.freedesktop.org/Fahien/gfx-pps>. The key is making it easy for developers to use. Ideally, perfetto is eventually available by default in mesa so that if your system hasperfettotraced running, you just need to run perfetto (perhaps along with setting an environment variable) with the mesa categories to see: - GPU processing timeline events. - GPU counters. - CPU events for potentially slow functions in mesa like shadercompiles.Example of what this data might look like (with fake GPU events): [image: percetto-gpu-example.png] *Runtime Characteristics* - ~500KB additional binary size. Even with using only the basicfeaturesof perfetto, it will increase the binary size of mesa by about 500KB. - Background thread. Perfetto uses a background thread forcommunicationwith the system tracing daemon (traced) to advertise trace data andgetnotification of trace start/stop. - Runtime overhead when disabled is designed to be optimal with one predicted branch, typically a few CPU cycles <https://perfetto.dev/docs/instrumentation/track-events#performance>perevent. While enabled, the overhead can be around 1 us per event. *Integration Challenges* - The perfetto SDK is C++ and designed around macros, lambdas, inline templates, etc. There are ongoing discussions on providing an official perfetto C API, but it is not yet clear when this will land on theperfettoroadmap. - The perfetto SDK is an amalgamated .h and .cc that adds up to 100K lines of code. - Anything that includes perfetto.h takes a long time to compile. - The current Perfetto SDK design is incompatible with being a shared library behind a C API. *Percetto* The percetto library <https://github.com/olvaffe/percetto> was recently implemented to provide an interim C API for perfetto. It providesefficientsupport for scoped trace events, multiple categories, counters, custom timestamps, and debug data annotations. Percetto also provides some features that are important to mesa, but not available yet with perfetto SDK: - Trace events from multiple perfetto instances in separate shared libraries (like mesa and virglrenderer) show correctly in a singleprocessand thread view. - Counter tracks and macro API. Percetto is missing API for perfetto's GPU DataSource and countersupport,but that feature could be implemented next if it is important for mesa. With the existing percetto API mesa could present GPU trace data as named 'slice' events and int64_t counters with custom timestamps as shown intheimage above (based on this sample <https://github.com/olvaffe/percetto/blob/main/examples/timestamps.c>). *Mesa Integration Alternatives* Note: we have some pressing needs for performance analysis in Chrome OS,soI'm intentionally leaving out the alternative of waiting for an official perfetto C API. Of course, once that C API is available it would becomeanoption to migrate to it from any of the alternatives below. Ordered by difficulty with easiest first: 1. Statically link with percetto as an optional external dependency (virglrenderer now has this approach <https://gitlab.freedesktop.org/virgl/virglrenderer/-/merge_requests/480>). - Pros: API already supports most common tracing needs. Tested andusedby an increasing number of CrOS components. - Cons: External dependency for optional mesa build option. 2. Embed Perfetto SDK + a Percetto fork/copy. - Pros: API already supports most common tracing needs. No added external dependency for mesa. - Cons: Percetto code divergence, bug fixes need to land in twotrees.3. Embed Perfetto SDK + custom C wrapper. - Pros: Tailored API for mesa's needs. - Cons: Nontrivial development efforts and maintenance. 4. Generate C stubs for the Perfetto protobuf and reimplement the Perfetto SDK in C. - Pros: Tailored API for mesa's needs. Possible smaller binaryimpactfrom simpler implementation. - Cons: Significant development efforts and maintenance. Regardless of the integration direction, I expect we would disableperfettoin the default build for now to minimize disruption. I like #1, because there are some nontrivial subtleties to the C wrapper that provide both API conveniences and runtime performance that wouldneedto be reimplemented or maintained with the other options. I will also volunteer to do #1 or #2, but I'm not sure I have time for #3 or #4 :D. Any other thoughts on how best to integrate perfetto into mesa? -jb _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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