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drm/xe: Thread prefetch of SVM ranges

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The migrate_vma_* functions are very CPU-intensive; as a result,
prefetching SVM ranges is limited by CPU performance rather than paging
copy engine bandwidth. To accelerate SVM range prefetching, the step
that calls migrate_vma_* is now threaded. A dedicated prefetch
workqueue is used for threading so prefetch work is never mixed with
page fault or garbage collector work.

Running xe_exec_system_allocator --r prefetch-benchmark, which tests
64MB prefetches, shows an increase from ~4.35 GB/s to 12.25 GB/s with
this patch on drm-tip. Enabling high SLPC further increases throughput
to ~15.25 GB/s, and combining SLPC with ULLS raises it to ~16 GB/s. Both
of these optimizations are upcoming.

Since the dedicated prefetch workqueue is not shared with page fault
or SVM garbage collector work, page fault servicing and garbage
collection can keep using a plain down_read() on vm->lock: there is no
risk of a blocked reader starving a worker that a pending writer is
waiting to flush, because that flushing is now confined to the
separate prefetch workqueue.

Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patch.msgid.link/20260806185202.3922432-4-matthew.brost@intel.com
This commit is contained in:
Matthew Brost 2026-08-06 11:51:53 -07:00
commit 65d3bfa42c
7 changed files with 167 additions and 58 deletions
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