[PATCH v6 00/34] GPU scheduler for i915 driver

John.C.Harrison
2016-04-20T17:13:57Z

Implemented a batch buffer submission scheduler for the i915 DRM driver.

The general theory of operation is that when batch buffers are
submitted to the driver, the execbuffer() code assigns a unique seqno
value and then packages up all the information required to execute the
batch buffer at a later time. This package is given over to the
scheduler which adds it to an internal node list. The scheduler also
scans the list of objects associated with the batch buffer and
compares them against the objects already in use by other buffers in
the node list. If matches are found then the new batch buffer node is
marked as being dependent upon the matching node. The same is done for
the context object. The scheduler also bumps up the priority of such
matching nodes on the grounds that the more dependencies a given batch
buffer has the more important it is likely to be.

The scheduler aims to have a given (tuneable) number of batch buffers
in flight on the hardware at any given time. If fewer than this are
currently executing when a new node is queued, then the node is passed
straight through to the submit function. Otherwise it is simply added
to the queue and the driver returns back to user land.

As each batch buffer completes, it raises an interrupt which wakes up
the scheduler. Note that it is possible for multiple buffers to
complete before the IRQ handler gets to run. Further, the seqno values
of the individual buffers are not necessary incrementing as the
scheduler may have re-ordered their submission. However, the scheduler
keeps the list of executing buffers in order of hardware submission.
Thus it can scan through the list until a matching seqno is found and
then mark all in flight nodes from that point on as completed.

A deferred work queue is also poked by the interrupt handler. When
this wakes up it can do more involved processing such as actually
removing completed nodes from the queue and freeing up the resources
associated with them (internal memory allocations, DRM object
references, context reference, etc.). The work handler also checks the
in flight count and calls the submission code if a new slot has
appeared.

When the scheduler's submit code is called, it scans the queued node
list for the highest priority node that has no unmet dependencies.
Note that the dependency calculation is complex as it must take
inter-ring dependencies and potential preemptions into account. Note
also that in the future this will be extended to include external
dependencies such as the Android Native Sync file descriptors and/or
the linux dma-buff synchronisation scheme.

If a suitable node is found then it is sent to execbuff_final() for
submission to the hardware. The in flight count is then re-checked and
a new node popped from the list if appropriate.

The scheduler also allows high priority batch buffers (e.g. from a
desktop compositor) to jump ahead of whatever is already running if
the underlying hardware supports pre-emption. In this situation, any
work that was pre-empted is returned to the queued list ready to be
resubmitted when no more high priority work is outstanding.

Various IGT tests are in progress to test the scheduler's operation
and will follow.

v2: Updated for changes in struct fence patch series and other changes
to underlying tree (e.g. removal of cliprects). Also changed priority
levels to be signed +/-1023 range and reduced mutex lock usage.

v3: More reuse of cached pointers rather than repeated dereferencing
(David Gordon).

Moved the dependency generation code out to a seperate function for
easier readability. Also added in support for the read-read
optimisation.

Major simplification of the DRM file close handler.

Fixed up an overzealous WARN.

Removed unnecessary flushing of the scheduler queue when waiting for a
request.

v4: Removed user land fence/sync integration as this is dependent upon
the de-staging of the Android sync code. That de-staging is now being
done by someone else. The sync support will be added back in to the
scheduler in a separate patch series which must wait for the
de-staging to be landed first.

Added support for killing batches from contexts that were banned after
the batches were submitted to the scheduler.

Changed various comments to fix typos, update to reflect changes to
the code, correct formatting and line wrapping, etc. Also wrapped
various long lines and twiddled white space to keep the style checker
happy.

Changed a bunch of BUG_ONs to WARN_ONs as apparently the latter are
preferred.

Used the correct array memory allocator function (kmalloc_array
instead of kmalloc).

Fixed a variable type (review comment by Joonas).

Fixed a WARN_ON firing incorrectly when removing killed nodes from the
scheduler's queue.

Dropped register definition update patch from this series. The changes
are all for pre-emption so it makes more sense for it to be part of
that series instead.

v5: Reverted power management changes as they apparently conflict with
mutex acquisition. Converted the override mask module parameter to a
set of boolean enable flags (just one in this patch set, but others
are added later for controlling pre-emption). [Chris Wilson]

Removed lots of whitespace from i915_scheduler.c and re-ordered it to
remove all forward declarations. Squashed down the i915_scheduler.c
sections of various patches into the initial 'start of scheduler'
patch. Thus the later patches simply hook in existing code into
various parts of the driver rather than adding the code as well. Added
documentation to various functions. Re-worked the submit function in
terms of mutex locking, error handling and exit paths. Split the
delayed work handler function in half. Made use of the kernel 'clamp'
macro. [Joonas Lahtinen]

Dropped the 'immediate submission' override option. This was a half
way house between full scheduler and direct submission and was only
really useful during early debug.

Added a re-install of the scheduler's interrupt hook around GPU reset.
[Zhipeng Gong]

Used lighter weight spinlocks.

v6: Updated to newer nightly (lots of ring -> engine renaming).

Added 'for_each_scheduler_node()' and 'assert_scheduler_lock_held()'
helper macros. Renamed 'i915_gem_execbuff_release_batch_obj' to
'i915_gem_execbuf_release_batch_obj'. Updated to use 'to_i915()'
instead of dev_private. Converted all enum labels to uppercase.
Removed various unnecessary WARNs. Renamed 'saved_objects' to just
'objs'. More code refactoring. Removed even more white space. Added
an i915_scheduler_destroy() function instead of doing explicit clean
up of scheduler internals from i915_driver_unload(). Changed extra
boolean i915_wait_request() parameter to a flags word and consumed the
original boolean parameter too. Also, replaced the
i915_scheduler_is_request_tracked() function with
i915_scheduler_is_mutex_required() and
i915_scheduler_is_request_batch_buffer() as the need for the former
has gone away and it was really being used to ask the latter two
questions in a convoluted manner. Wrapped boolean 'flush' parameter to
intel_engine_idle() with an _flush() macro.
[review feedback from Joonas Lahtinen]

Moved scheduler modue parameter declaration to correct place in
i915_params struct. [review feedback from Matt Roper]

Added an admin only check when setting the tuning parameters via
debugfs to prevent rogue user code trying to break the system with
strange settings. [review feedback from Jesse Barnes]

Added kerneldoc for intel_engine_idle().

Added running totals of 'flying' and 'queued' nodes rather than
re-calculating each time as a minor CPU performance optimisation.

Removed support for out of order seqno completion. All the prep work
patch series (seqno to request conversion, late seqno assignment,
etc.) that has now been done means that the scheduler no longer
generates out of order seqno completions. Thus all the complex code
for coping with such is no longer required and can be removed.

Fixed a bug in scheduler bypass mode introduced in the clean up code
refactoring of v5. The clean up function was seeing the node in the
wrong state and thus refusing to process it.

Improved the throttle by file handle feature by chaning from a simple
'return to userland when full' scheme with a 'sleep on request'
scheme. The former could lead to the busy polling and wasting lots of
CPU time as user land continuously retried the execbuf IOCTL in a
tight loop. Now the driver will sleep (without holding the mutex lock)
on the oldest request outstanding for that file and then automatically
retry. This is closer to the pre-scheduler behaviour of stalling on a
full ring buffer.

[Patches against drm-intel-nightly tree fetched 13/04/2016 with struct
fence conversion patches applied]

Dave Gordon (2):
drm/i915: Cache request pointer in *_submission_final()
drm/i915: Add scheduling priority to per-context parameters

John Harrison (32):
drm/i915: Add total count to context status debugfs output
drm/i915: Prelude to splitting i915_gem_do_execbuffer in two
drm/i915: Split i915_dem_do_execbuffer() in half
drm/i915: Re-instate request->uniq because it is extremely useful
drm/i915: Start of GPU scheduler
drm/i915: Disable hardware semaphores when GPU scheduler is enabled
drm/i915: Force MMIO flips when scheduler enabled
drm/i915: Added scheduler hook when closing DRM file handles
drm/i915: Added scheduler hook into i915_gem_request_notify()
drm/i915: Added deferred work handler for scheduler
drm/i915: Redirect execbuffer_final() via scheduler
drm/i915: Keep the reserved space mechanism happy
drm/i915: Added tracking/locking of batch buffer objects
drm/i915: Hook scheduler node clean up into retire requests
drm/i915: Added scheduler support to __wait_request() calls
drm/i915: Added scheduler support to page fault handler
drm/i915: Added scheduler flush calls to ring throttle and idle functions
drm/i915: Add scheduler hook to GPU reset
drm/i915: Added a module parameter to allow the scheduler to be disabled
drm/i915: Support for 'unflushed' ring idle
drm/i915: Defer seqno allocation until actual hardware submission time
drm/i915: Added trace points to scheduler
drm/i915: Added scheduler queue throttling by DRM file handle
drm/i915: Added debugfs interface to scheduler tuning parameters
drm/i915: Add early exit to execbuff_final() if insufficient ring space
drm/i915: Added scheduler statistic reporting to debugfs
drm/i915: Add scheduler support functions for TDR
drm/i915: Enable GPU scheduler by default
drm/i915: Add support for retro-actively banning batch buffers
drm/i915: Allow scheduler to manage inter-ring object synchronisation
drm/i915: Added debug state dump facilities to scheduler
drm/i915: Scheduler state dump via debugfs

drivers/gpu/drm/i915/Makefile | 1 +
drivers/gpu/drm/i915/i915_debugfs.c | 336 +++++-
drivers/gpu/drm/i915/i915_dma.c | 5 +
drivers/gpu/drm/i915/i915_drv.c | 9 +
drivers/gpu/drm/i915/i915_drv.h | 58 +-
drivers/gpu/drm/i915/i915_gem.c | 156 ++-
drivers/gpu/drm/i915/i915_gem_context.c | 24 +
drivers/gpu/drm/i915/i915_gem_execbuffer.c | 297 +++--
drivers/gpu/drm/i915/i915_params.c | 4 +
drivers/gpu/drm/i915/i915_params.h | 1 +
drivers/gpu/drm/i915/i915_scheduler.c | 1709 ++++++++++++++++++++++++++++
drivers/gpu/drm/i915/i915_scheduler.h | 180 +++
drivers/gpu/drm/i915/i915_trace.h | 225 +++-
drivers/gpu/drm/i915/intel_display.c | 10 +-
drivers/gpu/drm/i915/intel_lrc.c | 161 ++-
drivers/gpu/drm/i915/intel_lrc.h | 1 +
drivers/gpu/drm/i915/intel_ringbuffer.c | 69 +-
drivers/gpu/drm/i915/intel_ringbuffer.h | 5 +-
include/uapi/drm/i915_drm.h | 1 +
19 files changed, 3118 insertions(+), 134 deletions(-)
create mode 100644 drivers/gpu/drm/i915/i915_scheduler.c
create mode 100644 drivers/gpu/drm/i915/i915_scheduler.h