190 lines
6.6 KiB
ReStructuredText
190 lines
6.6 KiB
ReStructuredText
.. _drm-client-usage-stats:
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======================
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DRM client usage stats
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======================
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DRM drivers can choose to export partly standardised text output via the
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`fops->show_fdinfo()` as part of the driver specific file operations registered
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in the `struct drm_driver` object registered with the DRM core.
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One purpose of this output is to enable writing as generic as practically
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feasible `top(1)` like userspace monitoring tools.
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Given the differences between various DRM drivers the specification of the
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output is split between common and driver specific parts. Having said that,
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wherever possible effort should still be made to standardise as much as
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possible.
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File format specification
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=========================
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- File shall contain one key value pair per one line of text.
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- Colon character (`:`) must be used to delimit keys and values.
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- All keys shall be prefixed with `drm-`.
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- Whitespace between the delimiter and first non-whitespace character shall be
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ignored when parsing.
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- Keys are not allowed to contain whitespace characters.
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- Numerical key value pairs can end with optional unit string.
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- Data type of the value is fixed as defined in the specification.
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Key types
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---------
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1. Mandatory, fully standardised.
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2. Optional, fully standardised.
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3. Driver specific.
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Data types
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----------
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- <uint> - Unsigned integer without defining the maximum value.
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- <keystr> - String excluding any above defined reserved characters or whitespace.
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- <valstr> - String.
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Mandatory fully standardised keys
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---------------------------------
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- drm-driver: <valstr>
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String shall contain the name this driver registered as via the respective
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`struct drm_driver` data structure.
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Optional fully standardised keys
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--------------------------------
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Identification
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^^^^^^^^^^^^^^
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- drm-pdev: <aaaa:bb.cc.d>
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For PCI devices this should contain the PCI slot address of the device in
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question.
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- drm-client-id: <uint>
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Unique value relating to the open DRM file descriptor used to distinguish
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duplicated and shared file descriptors. Conceptually the value should map 1:1
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to the in kernel representation of `struct drm_file` instances.
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Uniqueness of the value shall be either globally unique, or unique within the
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scope of each device, in which case `drm-pdev` shall be present as well.
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Userspace should make sure to not double account any usage statistics by using
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the above described criteria in order to associate data to individual clients.
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Utilization
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^^^^^^^^^^^
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- drm-engine-<keystr>: <uint> ns
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GPUs usually contain multiple execution engines. Each shall be given a stable
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and unique name (keystr), with possible values documented in the driver specific
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documentation.
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Value shall be in specified time units which the respective GPU engine spent
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busy executing workloads belonging to this client.
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Values are not required to be constantly monotonic if it makes the driver
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implementation easier, but are required to catch up with the previously reported
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larger value within a reasonable period. Upon observing a value lower than what
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was previously read, userspace is expected to stay with that larger previous
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value until a monotonic update is seen.
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- drm-engine-capacity-<keystr>: <uint>
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Engine identifier string must be the same as the one specified in the
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drm-engine-<keystr> tag and shall contain a greater than zero number in case the
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exported engine corresponds to a group of identical hardware engines.
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In the absence of this tag parser shall assume capacity of one. Zero capacity
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is not allowed.
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- drm-cycles-<keystr>: <uint>
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Engine identifier string must be the same as the one specified in the
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drm-engine-<keystr> tag and shall contain the number of busy cycles for the given
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engine.
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Values are not required to be constantly monotonic if it makes the driver
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implementation easier, but are required to catch up with the previously reported
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larger value within a reasonable period. Upon observing a value lower than what
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was previously read, userspace is expected to stay with that larger previous
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value until a monotonic update is seen.
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- drm-total-cycles-<keystr>: <uint>
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Engine identifier string must be the same as the one specified in the
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drm-cycles-<keystr> tag and shall contain the total number cycles for the given
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engine.
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This is a timestamp in GPU unspecified unit that matches the update rate
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of drm-cycles-<keystr>. For drivers that implement this interface, the engine
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utilization can be calculated entirely on the GPU clock domain, without
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considering the CPU sleep time between 2 samples.
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A driver may implement either this key or drm-maxfreq-<keystr>, but not both.
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- drm-maxfreq-<keystr>: <uint> [Hz|MHz|KHz]
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Engine identifier string must be the same as the one specified in the
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drm-engine-<keystr> tag and shall contain the maximum frequency for the given
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engine. Taken together with drm-cycles-<keystr>, this can be used to calculate
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percentage utilization of the engine, whereas drm-engine-<keystr> only reflects
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time active without considering what frequency the engine is operating as a
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percentage of its maximum frequency.
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A driver may implement either this key or drm-total-cycles-<keystr>, but not
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both.
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Memory
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^^^^^^
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- drm-memory-<region>: <uint> [KiB|MiB]
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Each possible memory type which can be used to store buffer objects by the
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GPU in question shall be given a stable and unique name to be returned as the
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string here. The name "memory" is reserved to refer to normal system memory.
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Value shall reflect the amount of storage currently consumed by the buffer
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objects belong to this client, in the respective memory region.
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Default unit shall be bytes with optional unit specifiers of 'KiB' or 'MiB'
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indicating kibi- or mebi-bytes.
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- drm-shared-<region>: <uint> [KiB|MiB]
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The total size of buffers that are shared with another file (e.g., have more
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than a single handle).
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- drm-total-<region>: <uint> [KiB|MiB]
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The total size of buffers that including shared and private memory.
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- drm-resident-<region>: <uint> [KiB|MiB]
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The total size of buffers that are resident in the specified region.
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- drm-purgeable-<region>: <uint> [KiB|MiB]
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The total size of buffers that are purgeable.
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- drm-active-<region>: <uint> [KiB|MiB]
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The total size of buffers that are active on one or more engines.
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Implementation Details
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======================
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Drivers should use drm_show_fdinfo() in their `struct file_operations`, and
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implement &drm_driver.show_fdinfo if they wish to provide any stats which
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are not provided by drm_show_fdinfo(). But even driver specific stats should
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be documented above and where possible, aligned with other drivers.
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Driver specific implementations
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-------------------------------
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* :ref:`i915-usage-stats`
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* :ref:`panfrost-usage-stats`
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* :ref:`xe-usage-stats`
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