drm/xe: Chain page faults via queue-resident cache to avoid fault storms

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Some Xe platforms can generate pagefault storms where many faults target
the same address range in a short time window (e.g. many EU threads
faulting the same page). The current worker/locking model effectively
serializes faults for a given range and repeatedly performs VMA/range
lookups for each fault, which creates head-of-queue blocking and wastes
CPU in the hot path.

Introduce a page fault chaining cache that coalesces faults targeting
the same ASID and address range.

Each worker tracks the active fault range it is servicing. Fault entries
reside in stable queue storage, allowing the IRQ handler to match new
faults against the worker cache and directly chain cache hits onto the
active entry without allocation or waiting for dequeue. Once the leading
fault completes, the worker acknowledges the entire chain.

A small allocation state is added to each entry so queue, worker, and
IRQ paths can safely reference the same fault object. This prevents
reuse while the fault is active and guarantees that chained faults
remain valid until acknowledged.

Fault handlers also record the serviced range so subsequent faults can
be acknowledged without re-running the full resolution path.

This removes repeated fault resolution during fault storms and
significantly improves forward progress in SVM workloads.

Since threaded prefetches now use a dedicated prefetch workqueue
(usm.prefetch_wq) rather than sharing the page fault workqueue, page
fault servicing can no longer deadlock on vm->lock, so this cache does
not need an -EAGAIN retry path for a failed vm->lock acquisition.

Assisted-by: ChatGPT:gpt-5 # Documentation
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patch.msgid.link/20260806185202.3922432-9-matthew.brost@intel.com

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This commit is contained in:

Matthew Brost 2026-08-06 11:51:58 -07:00

parent 107156dc6b

commit f2b4b3f814

5 changed files with 527 additions and 85 deletions

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437

drivers/gpu/drm/xe/xe_pagefault.c

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71

drivers/gpu/drm/xe/xe_pagefault.h

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81

drivers/gpu/drm/xe/xe_pagefault_types.h

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16

drivers/gpu/drm/xe/xe_svm.c

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9

drivers/gpu/drm/xe/xe_svm.h

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