[RFC,8/8] drm: Document fdinfo format specification

Commit Message

Tvrtko Ursulin July 12, 2021, 12:17 p.m. UTC

From: Tvrtko Ursulin <[e-mail]>

Proposal to standardise the fdinfo text format as optionally output by DRM
drivers.

Idea is that a simple but, well defined, spec will enable generic
userspace tools to be written while at the same time avoiding a more heavy
handed approach of adding a mid-layer to DRM.

i915 implements a subset of the spec, everything apart from the memory
stats currently, and a matching intel_gpu_top tool exists.

Open is to see if AMD can migrate to using the proposed GPU utilisation
key-value pairs, or if they are not workable to see whether to go
vendor specific, or if a standardised  alternative can be found which is
workable for both drivers.

Same for the memory utilisation key-value pairs proposal.

Signed-off-by: Tvrtko Ursulin <[e-mail]>
Cc: David M Nieto <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
---
 Documentation/gpu/drm-usage-stats.rst | 99 +++++++++++++++++++++++++++
 Documentation/gpu/i915.rst            | 27 ++++++++
 Documentation/gpu/index.rst           |  1 +
 3 files changed, 127 insertions(+)
 create mode 100644 Documentation/gpu/drm-usage-stats.rst

Patch

diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst
new file mode 100644
index 000000000000..d35e4a01bc5b
--- /dev/null
+++ b/Documentation/gpu/drm-usage-stats.rst
@@ -0,0 +1,99 @@ 
+.. _drm-client-usage-stats:
+
+======================
+DRM client usage stats
+======================
+
+DRM drivers can choose to export partly standardised text output via the
+`fops->show_fdinfo()` as part of the driver specific file operations registered
+in the `struct drm_driver` object registered with the DRM core.
+
+One purpose of this output is to enable writing as generic as practicaly
+feasible `top(1)` like userspace monitoring tools.
+
+Given the differences between various DRM drivers the specification of the
+output is split between common and driver specific parts. Having said that,
+wherever possible effort should still be made to standardise as much as
+possible.
+
+File format specification
+=========================
+
+- File shall contain one key value pair per one line of text.
+- Colon character (`:`) must be used to delimit keys and values.
+- All keys shall be prefixed with `drm-`.
+- Whitespace between the delimiter and first non-whitespace character shall be
+  ignored when parsing.
+- Neither keys or values are allowed to contain whitespace characters.
+- Numerical key value pairs can end with optional unit string.
+- Data type of the value is fixed as defined in the specification.
+
+Key types
+---------
+
+1. Mandatory, fully standardised.
+2. Optional, fully standardised.
+3. Driver specific.
+
+Mandatory fully standardised keys
+---------------------------------
+
+- drm-driver: <string>
+
+String shall contain a fixed string uniquely identified the driver handling
+the device in question. For example name of the respective kernel module.
+
+Optional fully standardised keys
+--------------------------------
+
+- drm-pdev: <aaaa:bb.cc.d>
+
+For PCI devices this should contain the PCI slot address of the device in
+question.
+
+- drm-client-id: <uint>
+
+Unique value relating to the open DRM file descriptor used to distinguish
+duplicated and shared file descriptors. Conceptually the value should map 1:1
+to the in kernel representation of `struct drm_file` instances.
+
+Uniqueness of the value shall be either globally unique, or unique within the
+scope of each device, in which case `drm-pdev` shall be present as well.
+
+Userspace should make sure to not double account any usage statistics by using
+the above described criteria in order to associate data to individual clients.
+
+- drm-client-name: <string>
+
+Process name of the thread which opened the file.
+
+- drm-client-pid: <uint>
+
+PID of the thread which opened the file.
+
+- drm-engine-<str>: <uint> ns
+
+GPUs usually contain multiple execution engines. Each shall be given a stable
+and unique string, with possible values documented in the driver specific
+specification document.
+
+Value shall be a monotonically increasing number of nanoseconds the respective
+GPU engine spent executing workloads belonging to this client.
+
+- drm-memory-<str>: <uint> [KiB|MiB]
+
+Each possible memory type which can be used to store buffer objects by the
+GPU in question shall be given a stable and unique name to be returned as the
+string here.
+
+Value shall reflect the amount of storage currently consumed by the buffer
+object belong to this client, in the respective memory region.
+
+Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
+indicating kibi- or mebi-bytes.
+
+===============================
+Driver specific implementations
+===============================
+
+:ref:`i915-usage-stats`
diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst
index 204ebdaadb45..2bfd2441576e 100644
--- a/Documentation/gpu/i915.rst
+++ b/Documentation/gpu/i915.rst
@@ -701,3 +701,30 @@  The style guide for ``i915_reg.h``.
 
 .. kernel-doc:: drivers/gpu/drm/i915/i915_reg.h
    :doc: The i915 register macro definition style guide
+
+.. _i915-usage-stats:
+
+i915 DRM client usage stats implementation
+==========================================
+
+The drm/i915 drivers implements the DRM client usage stats specification as
+documented in :ref:`drm-client-usage-stats`.
+
+Example of the output showing the implemented key value pairs and entirety of
+the currenly possible format options:
+
+::
+
+      pos:    0
+      flags:  0100002
+      mnt_id: 21
+      drm-driver: i915
+      drm-pdev:   0000:00:02.0
+      drm-client-id:      7
+      drm-engine-render:  9288864723 ns
+      drm-engine-copy:    2035071108 ns
+      drm-engine-video:   0 ns
+      drm-engine-video-enhance:   0 ns
+
+Possible `drm-engine-` key names are: `render`, `copy`, `video` and
+`video-enhance`.
diff --git a/Documentation/gpu/index.rst b/Documentation/gpu/index.rst
index b9c1214d8f23..b99dede9a5b1 100644
--- a/Documentation/gpu/index.rst
+++ b/Documentation/gpu/index.rst
@@ -10,6 +10,7 @@  Linux GPU Driver Developer's Guide
    drm-kms
    drm-kms-helpers
    drm-uapi
+   drm-usage-stats
    driver-uapi
    drm-client
    drivers