From 2d12d3da5374433d44692a8681417bc7c424439b Mon Sep 17 00:00:00 2001 From: Tvrtko Ursulin Date: Fri, 1 Apr 2022 15:22:03 +0100 Subject: [PATCH] drm: Document fdinfo format specification MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. v2: * Update for removal of name and pid. v3: * 'Drm-driver' tag will be obtained from struct drm_driver.name. (Daniel) v4: * Added drm-engine-capacity- tag. Signed-off-by: Tvrtko Ursulin Cc: David M Nieto Cc: Christian König Cc: Daniel Vetter Cc: Daniel Stone Cc: Chris Healy Acked-by: Christian König Reviewed-by: Umesh Nerlige Ramappa Link: https://patchwork.freedesktop.org/patch/msgid/20220401142205.3123159-7-tvrtko.ursulin@linux.intel.com --- Documentation/gpu/drm-usage-stats.rst | 106 ++++++++++++++++++++++++++ Documentation/gpu/index.rst | 1 + 2 files changed, 107 insertions(+) create mode 100644 Documentation/gpu/drm-usage-stats.rst diff --git a/Documentation/gpu/drm-usage-stats.rst b/Documentation/gpu/drm-usage-stats.rst new file mode 100644 index 000000000000..b8cc28f4da6f --- /dev/null +++ b/Documentation/gpu/drm-usage-stats.rst @@ -0,0 +1,106 @@ +.. _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. + +Data types +---------- + +- - Unsigned integer without defining the maximum value. +- - String excluding any above defined reserved characters or whitespace. + +Mandatory fully standardised keys +--------------------------------- + +- drm-driver: + +String shall contain the name this driver registered as via the respective +`struct drm_driver` data structure. + +Optional fully standardised keys +-------------------------------- + +- drm-pdev: + +For PCI devices this should contain the PCI slot address of the device in +question. + +- drm-client-id: + +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-engine-: ns + +GPUs usually contain multiple execution engines. Each shall be given a stable +and unique name (str), with possible values documented in the driver specific +documentation. + +Value shall be in specified time units which the respective GPU engine spent +busy executing workloads belonging to this client. + +Values are not required to be constantly monotonic if it makes the driver +implementation easier, but are required to catch up with the previously reported +larger value within a reasonable period. Upon observing a value lower than what +was previously read, userspace is expected to stay with that larger previous +value until a monotonic update is seen. + +- drm-engine-capacity-: + +Engine identifier string must be the same as the one specified in the +drm-engine- tag and shall contain a greater than zero number in case the +exported engine corresponds to a group of identical hardware engines. + +In the absence of this tag parser shall assume capacity of one. Zero capacity +is not allowed. + +- drm-memory-: [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. 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