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This CL adds some info about the different backends and tracing/logging,
and marks some sections as applying only to the legacy API.

A rendered version of the resulting MD can be found in [1] (using
gerrit as a git server).

[1] https://chromium.googlesource.com/chromium/src.git/+/refs/changes/95/3203095/1/docs/gpu/vaapi.md

Change-Id: I4c632a76fcdb25e96b017f180321bb41e6990f3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3203095
Commit-Queue: Jao-ke Chin-Lee <jchinlee@chromium.org>
Auto-Submit: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Jao-ke Chin-Lee <jchinlee@chromium.org>
Cr-Commit-Position: refs/heads/main@{#928227}
This commit is contained in:
Miguel Casas
2021-10-05 17:41:43 +00:00
committed by Chromium LUCI CQ
parent 633715b23c
commit 32c29a4339
1 changed files with 73 additions and 49 deletions

122
docs/gpu/vaapi.md

@ -1,24 +1,88 @@
# VaAPI
# VA-API
This page documents tracing and debugging the Video Acceleration API (VaAPI or
VA-API) on ChromeOS. The VA-API is an open-source library and API specification,
VA-API) on ChromeOS. VA-API is an open-source library and API specification,
providing access to graphics hardware acceleration capabilities for video and
image processing. The VaAPI is used on ChromeOS on both Intel and AMD platforms.
image processing. VA-API is used on ChromeOS on both Intel and AMD platforms.
[TOC]
## Overview
VA-API is implemented by a generic `libva` library, developed upstream on
the [VaAPI GitHub repository], from which ChromeOS is a downstream client via
the [libva] package. Several backends are available for it, notably the legacy
[Intel i965], the modern [Intel iHD] and the [AMD].
VaAPI code is developed upstream on the [VaAPI GitHub repository], from which
ChromeOS is a downstream client via the [libva] package, with packaged backends
for e.g. both [Intel] and [AMD].
![](https://i.imgur.com/skS8Ged.png)
[VaAPI GitHub repository]: https://github.com/intel/libva
[libva]: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/main/x11-libs/libva/
[Intel]: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/main/x11-libs/libva-intel-driver/
[Intel i965]: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/main/x11-libs/libva-intel-driver/
[Intel iHD]: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/main/x11-libs/libva-intel-media-driver/
[AMD]: https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/main/media-libs/libva-amdgpu-driver/
## Tracing VaAPI video decoding
## `libva` tracing
The environment variable `LIBVA_TRACE=/path/to/file` can be exposed to libva to
store tracing information (see [va_trace.c]). `libva` will create a number of
e.g. `libva.log.033807.thd-0x00000b25 ` files (one per thread) with a list of
the actions taken and semi-disassembled parameters.
[va_trace.c]: https://github.com/intel/libva/blob/64520e9ec90ed30e016d7c633d746b3bf538c702/va/va_trace.c#L59
### `libva` logging
The environment variable `LIBVA_MESSAGING_LEVEL=0` (or `1` or `2`) can be used
to configure increasing logging verbosity to stdout (see [va.c]). Chromium uses
a level `0` by default in `vaapi_wrapper.cc`.
[va.c]: https://github.com/intel/libva/blob/2ece7099061ba4ea821545c8b6712b5c421c4dea/va/va.c#L194
### Tracing power consumption
Power consumption is available on ChromeOS test/dev images via the command line
binary [`dump_intel_rapl_consumption`]; this tool averages the power
consumption of the four SoC domains over a configurable period of time, usually
a few seconds. These domains are, in the order presented by the tool:
* `pkg`: estimated power consumption of the whole SoC; in particular, this is a
superset of pp0 and pp1, including all accessory silicon, e.g. video
processing.
* `pp0`: CPU set.
* `pp1`/`gfx`: Integrated GPU or GPUs.
* `dram`: estimated power consumption of the DRAM, from the bus activity.
`dump_intel_rapl_consumption` results should be a subset and of the same
numerical value as those produced with e.g. `turbostat`. Note that despite the
name, the tool works on AMD platforms as well, since they provide the same type
of measurement registers, albeit a subset of Intel's. Googlers can read more
about this topic under [go/power-consumption-meas-in-intel].
`dump_intel_rapl_consumption` is usually run while a given workload is active
(e.g. a video playback) with an interval larger than a second to smooth out all
kinds of system services that would show up in smaller periods, e.g. WiFi.
```shell
dump_intel_rapl_consumption --interval_ms=2000 --repeat --verbose
```
E.g. on a nocturne main1, the average power consumption while playing back the
first minute of a 1080p VP9 [video], the average consumptions in watts are:
|`pkg` |`pp0` |`pp1`/`gfx` |`dram`|
| ---: | ---: | ---: | ---: |
| 2.63 | 1.44 | 0.29 | 0.87 |
As can be seen, `pkg` ~= `pp0` + `pp1` + 1W, this extra watt is the cost of all
the associated silicon, e.g. bridges, bus controllers, caches, and the media
processing engine.
[`dump_intel_rapl_consumption`]: https://chromium.googlesource.com/chromiumos/platform2/+/main/power_manager/tools/dump_intel_rapl_consumption.cc
[video]: https://commons.wikimedia.org/wiki/File:Big_Buck_Bunny_4K.webm
[go/power-consumption-meas-in-intel]: http://go/power-consumption-meas-in-intel
## Tracing VaAPI video decoding (**LEGACY VDA API**)
A simplified diagram of the buffer circulation is provided below. The "client"
is always a Renderer process via a Mojo/IPC communication. Essentially the VaAPI
@ -105,46 +169,6 @@ the desired `context_group` can be tricky.
[the probe-gpu example]: https://chromium.googlesource.com/chromium/src/+/HEAD/docs/memory-infra/probe-gpu.md#example
[crbug.com/721674]: https://crbug.com/721674
### Tracing power consumption
Power consumption is available on ChromeOS test/dev images via the command line
binary [`dump_intel_rapl_consumption`]; this tool averages the power
consumption of the four SoC domains over a configurable period of time, usually
a few seconds. These domains are, in the order presented by the tool:
* `pkg`: estimated power consumption of the whole SoC; in particular, this is a
superset of pp0 and pp1, including all accessory silicon, e.g. video
processing.
* `pp0`: CPU set.
* `pp1`/`gfx`: Integrated GPU or GPUs.
* `dram`: estimated power consumption of the DRAM, from the bus activity.
Googlers can read more about this topic under
[go/power-consumption-meas-in-intel].
`dump_intel_rapl_consumption` is usually run while a given workload is active
(e.g. a video playback) with an interval larger than a second to smooth out all
kinds of system services that would show up in smaller periods, e.g. WiFi.
```shell
dump_intel_rapl_consumption --interval_ms=2000 --repeat --verbose
```
E.g. on a nocturne main1, the average power consumption while playing back the
first minute of a 1080p VP9 [video], the average consumptions in watts are:
|`pkg` |`pp0` |`pp1`/`gfx` |`dram`|
| ---: | ---: | ---: | ---: |
| 2.63 | 1.44 | 0.29 | 0.87 |
As can be seen, `pkg` ~= `pp0` + `pp1` + 1W, this extra watt is the cost of all
the associated silicon, e.g. bridges, bus controllers, caches, and the media
processing engine.
[`dump_intel_rapl_consumption`]: https://chromium.googlesource.com/chromiumos/platform2/+/main/power_manager/tools/dump_intel_rapl_consumption.cc
[video]: https://commons.wikimedia.org/wiki/File:Big_Buck_Bunny_4K.webm
[go/power-consumption-meas-in-intel]: http://go/power-consumption-meas-in-intel
### Tracing CPU cycles and instantaneous buffer usage
TODO(mcasas): fill in this section.