BMC/Intel-BMC/linux.git/drivers/gpu/drm/i915/intel_context.c, branch dev-5.2

drm/i915: Make the semaphore saturation mask global

2019-07-31T05:25:03+00:00

commit 44d89409a12eb8333735958509d7d591b461d13d upstream. The idea behind keeping the saturation mask local to a context backfired spectacularly. The premise with the local mask was that we would be more proactive in attempting to use semaphores after each time the context idled, and that all new contexts would attempt to use semaphores ignoring the current state of the system. This turns out to be horribly optimistic. If the system state is still oversaturated and the existing workloads have all stopped using semaphores, the new workloads would attempt to use semaphores and be deprioritised behind real work. The new contexts would not switch off using semaphores until their initial batch of low priority work had completed. Given sufficient backload load of equal user priority, this would completely starve the new work of any GPU time. To compensate, remove the local tracking in favour of keeping it as global state on the engine -- once the system is saturated and semaphores are disabled, everyone stops attempting to use semaphores until the system is idle again. One of the reason for preferring local context tracking was that it worked with virtual engines, so for switching to global state we could either do a complete check of all the virtual siblings or simply disable semaphores for those requests. This takes the simpler approach of disabling semaphores on virtual engines. The downside is that the decision that the engine is saturated is a local measure -- we are only checking whether or not this context was scheduled in a timely fashion, it may be legitimately delayed due to user priorities. We still have the same dilemma though, that we do not want to employ the semaphore poll unless it will be used. v2: Explain why we need to assume the worst wrt virtual engines. Fixes: ca6e56f654e7 ("drm/i915: Disable semaphore busywaits on saturated systems") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Dmitry Rogozhkin Cc: Dmitry Ermilov Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190618074153.16055-8-chris@chris-wilson.co.uk Signed-off-by: Joonas Lahtinen Signed-off-by: Greg Kroah-Hartman

drm/i915: Disable semaphore busywaits on saturated systems

2019-05-07T09:46:19+00:00

Asking the GPU to busywait on a memory address, perhaps not unexpectedly in hindsight for a shared system, leads to bus contention that affects CPU programs trying to concurrently access memory. This can manifest as a drop in transcode throughput on highly over-saturated workloads. The only clue offered by perf, is that the bus-cycles (perf stat -e bus-cycles) jumped by 50% when enabling semaphores. This corresponds with extra CPU active cycles being attributed to intel_idle's mwait. This patch introduces a heuristic to try and detect when more than one client is submitting to the GPU pushing it into an oversaturated state. As we already keep track of when the semaphores are signaled, we can inspect their state on submitting the busywait batch and if we planned to use a semaphore but were too late, conclude that the GPU is overloaded and not try to use semaphores in future requests. In practice, this means we optimistically try to use semaphores for the first frame of a transcode job split over multiple engines, and fail if there are multiple clients active and continue not to use semaphores for the subsequent frames in the sequence. Periodically, we try to optimistically switch semaphores back on whenever the client waits to catch up with the transcode results. With 1 client, on Broxton J3455, with the relative fps normalized by %cpu: x no semaphores + drm-tip * patched +------------------------------------------------------------------------+ | * | | *+ | | **+ | | **+ x | | x * +**+ x | | x x * * +***x xx | | x x * * *+***x *x | | x x* + * * *****x *x x | | + x xx+x* + *** * ********* x * | | + x xx+x* * *** +** ********* xx * | | * + ++++* + x*x****+*+* ***+*************+x* * | |*+ +** *+ + +* + *++****** *xxx**********x***+*****************+*++ *| | |__________A_____M_____| | | |_______________A____M_________| | | |____________A___M________| | +------------------------------------------------------------------------+ N Min Max Median Avg Stddev x 120 2.60475 3.50941 3.31123 3.2143953 0.21117399 + 120 2.3826 3.57077 3.25101 3.1414161 0.28146407 Difference at 95.0% confidence -0.0729792 +/- 0.0629585 -2.27039% +/- 1.95864% (Student's t, pooled s = 0.248814) * 120 2.35536 3.66713 3.2849 3.2059917 0.24618565 No difference proven at 95.0% confidence With 10 clients over-saturating the pipeline: x no semaphores + drm-tip * patched +------------------------------------------------------------------------+ | ++ ** | | ++ ** | | ++ ** | | ++ ** | | ++ xx *** | | ++ xx *** | | ++ xxx*** | | ++ xxx*** | | +++ xxx*** | | +++ xx**** | | +++ xx**** | | +++ xx**** | | +++ xx**** | | ++++ xx**** | | +++++ xx**** | | +++++ x x****** | | ++++++ xxx******* | | ++++++ xxx******* | | ++++++ xxx******* | | ++++++ xx******** | | ++++++ xxxx******** | | ++++++ xxxx******** | | ++++++++ xxxxx********* | |+ + + + ++++++++ xxx*xx**********x* *| | |__A__| | | |__AM__| | | |__A_| | +------------------------------------------------------------------------+ N Min Max Median Avg Stddev x 120 2.47855 2.8972 2.72376 2.7193402 0.074604933 + 120 1.17367 1.77459 1.71977 1.6966782 0.085850697 Difference at 95.0% confidence -1.02266 +/- 0.0203502 -37.607% +/- 0.748352% (Student's t, pooled s = 0.0804246) * 120 2.57868 3.00821 2.80142 2.7923878 0.058646477 Difference at 95.0% confidence 0.0730476 +/- 0.0169791 2.68622% +/- 0.624383% (Student's t, pooled s = 0.0671018) Indicating that we've recovered the regression from enabling semaphores on this saturated setup, with a hint towards an overall improvement. Very similar, but of smaller magnitude, results are observed on both Skylake(gt2) and Kabylake(gt4). This may be due to the reduced impact of bus-cycles, where we see a 50% hit on Broxton, it is only 10% on the big core, in this particular test. One observation to make here is that for a greedy client trying to maximise its own throughput, using semaphores is the right choice. It is only the holistic system-wide view that semaphores of one client impacts another and reduces the overall throughput where we would choose to disable semaphores. The most noticeable negactive impact this has is on the no-op microbenchmarks, which are also very notable for having no cpu bus load. In particular, this increases the runtime and energy consumption of gem_exec_whisper. Fixes: e88619646971 ("drm/i915: Use HW semaphores for inter-engine synchronisation on gen8+") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Dmitry Rogozhkin Cc: Dmitry Ermilov Cc: Joonas Lahtinen Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190504070707.30902-1-chris@chris-wilson.co.uk (cherry picked from commit ca6e56f654e7b241256ffba78cd2abb22aa3bc97) Signed-off-by: Joonas Lahtinen

drm/i915: Hold a reference to the active HW context

2019-03-19T08:21:13+00:00

For virtual engines, we need to keep the HW context alive while it remains in use. For regular HW contexts, they are created and kept alive until the end of the GEM context. For simplicity, generalise the requirements and keep an active reference to each HW context. Signed-off-by: Chris Wilson Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190318212347.30146-2-chris@chris-wilson.co.uk

drm/i915: Lock the gem_context->active_list while dropping the link

2019-03-19T08:21:11+00:00

On unpinning the intel_context, we remove it from the active list inside the GEM context. This list is supposed to be guarded by the GEM context mutex, so remember to take it! Fixes: 7e3d9a59410d ("drm/i915: Track active engines within a context") Signed-off-by: Chris Wilson Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190318212347.30146-1-chris@chris-wilson.co.uk

drm/i915: Introduce intel_context.pin_mutex for pin management

2019-03-08T14:04:19+00:00

Introduce a mutex to start locking the HW contexts independently of struct_mutex, with a view to reducing the coarse struct_mutex. The intel_context.pin_mutex is used to guard the transition to and from being pinned on the gpu, and so is required before starting to build any request. The intel_context will then remain pinned until the request completes, but the mutex can be released immediately unpin completion of pinning the context. A slight variant of the above is used by per-context sseu that wants to inspect the pinned status of the context, and requires that it remains stable (either !pinned or pinned) across its operation. By using the pin_mutex to serialise operations while pin_count==0, we can take that pin_mutex for stabilise the boolean pin status. v2: for Tvrtko! * Improved commit message. * Dropped _gpu suffix from gen8_modify_rpcs_gpu. v3: Repair the locking for sseu selftests Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190308132522.21573-7-chris@chris-wilson.co.uk

drm/i915: Make context pinning part of intel_context_ops

2019-03-08T13:59:59+00:00

Push the intel_context pin callback down from intel_engine_cs onto the context itself by virtue of having a central caller for intel_context_pin() being able to lookup the intel_context itself. Signed-off-by: Chris Wilson Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190308132522.21573-5-chris@chris-wilson.co.uk

drm/i915: Move over to intel_context_lookup()

2019-03-08T13:59:52+00:00

In preparation for an ever growing number of engines and so ever increasing static array of HW contexts within the GEM context, move the array over to an rbtree, allocated upon first use. Unfortunately, this imposes an rbtree lookup at a few frequent callsites, but we should be able to mitigate those by moving over to using the HW context as our primary type and so only incur the lookup on the boundary with the user GEM context and engines. v2: Check for no HW context in guc_stage_desc_init Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190308132522.21573-4-chris@chris-wilson.co.uk