Add a description for the TLB cache invalidation algorithm and for the related kAPI functions.
Signed-off-by: Mauro Carvalho Chehab <mche...@kernel.org> --- To avoid mailbombing on a large number of people, only mailing lists were C/C on the cover. See [PATCH 0/2] at: https://lore.kernel.org/all/cover.1659011328.git.mche...@kernel.org/ drivers/gpu/drm/i915/gt/intel_tlb.c | 25 +++++++++ drivers/gpu/drm/i915/gt/intel_tlb.h | 83 +++++++++++++++++++++++++++++ 2 files changed, 108 insertions(+) diff --git a/drivers/gpu/drm/i915/gt/intel_tlb.c b/drivers/gpu/drm/i915/gt/intel_tlb.c index af8cae979489..d5df2e0f77fb 100644 --- a/drivers/gpu/drm/i915/gt/intel_tlb.c +++ b/drivers/gpu/drm/i915/gt/intel_tlb.c @@ -145,6 +145,18 @@ static void mmio_invalidate_full(struct intel_gt *gt) intel_uncore_forcewake_put_delayed(uncore, FORCEWAKE_ALL); } +/** + * intel_gt_invalidate_tlb_full - do full TLB cache invalidation + * @gt: GT structure + * @seqno: sequence number + * + * Do a full TLB cache invalidation if the @seqno is bigger than the last + * full TLB cache invalidation. + * + * Note: + * The TLB cache invalidation logic depends on GEN-specific registers. + * It currently supports GEN8 to GEN12 and GuC-based TLB cache invalidation. + */ void intel_gt_invalidate_tlb_full(struct intel_gt *gt, u32 seqno) { intel_wakeref_t wakeref; @@ -171,12 +183,25 @@ void intel_gt_invalidate_tlb_full(struct intel_gt *gt, u32 seqno) } } +/** + * intel_gt_init_tlb - initialize TLB-specific vars + * @gt: GT structure + * + * TLB cache invalidation logic internally uses some resources that require + * initialization. Should be called before doing any TLB cache invalidation. + */ void intel_gt_init_tlb(struct intel_gt *gt) { mutex_init(>->tlb.invalidate_lock); seqcount_mutex_init(>->tlb.seqno, >->tlb.invalidate_lock); } +/** + * intel_gt_fini_tlb - initialize TLB-specific vars + * @gt: GT structure + * + * Frees any resources needed by TLB cache invalidation logic. + */ void intel_gt_fini_tlb(struct intel_gt *gt) { mutex_destroy(>->tlb.invalidate_lock); diff --git a/drivers/gpu/drm/i915/gt/intel_tlb.h b/drivers/gpu/drm/i915/gt/intel_tlb.h index 46ce25bf5afe..d186f5d5901f 100644 --- a/drivers/gpu/drm/i915/gt/intel_tlb.h +++ b/drivers/gpu/drm/i915/gt/intel_tlb.h @@ -11,16 +11,99 @@ #include "intel_gt_types.h" +/** + * DOC: TLB cache invalidation logic + * + * The way the current algorithm works is that drm_i915_gem_object can be + * created on any order. At unbind/evict time, the object is warranted that + * it won't be used anymore. So, they store a sequence number provided by + * intel_gt_next_invalidate_tlb_full().This can happen either at + * __vma_put_pages(), for VMA sync unbind, or at ppgtt_unbind_vma(), for + * VMA async VMA bind. + * + * At __i915_gem_object_unset_pages(), intel_gt_invalidate_tlb() is called, + * where it checks if the sequence number of the object was already invalidated + * or not. If not, it increments it:: + * + * void intel_gt_invalidate_tlb(struct intel_gt *gt, u32 seqno) + * { + * ... + * with_intel_gt_pm_if_awake(gt, wakeref) { + * mutex_lock(>->tlb.invalidate_lock); + * if (tlb_seqno_passed(gt, seqno)) + * goto unlock; + * + * mmio_invalidate_full(gt); + * + * write_seqcount_invalidate(>->tlb.seqno); // increment seqno + * ... + * + * So, let's say the current seqno is 2 and 3 new objects were created, + * on this order: + * + * obj1 + * obj2 + * obj3 + * + * They can be unbind/evict on a different order. At unbind/evict time, + * the mm.tlb will be stamped with the sequence number, using the number + * from the last TLB flush, plus 1. + * + * Different threads may be used on unbind/evict and/or unset pages. + * + * As the logic at void intel_gt_invalidate_tlb() is protected by a mutex, + * for simplicity, let's consider just two threads:: + * + * sequence number Thread 0 Thread 1 + * + * seqno=2 + * unbind/evict event + * obj3.mm.tlb = seqno | 1 + * + * unbind/evict event + * obj1.mm.tlb = seqno | 1 + * __i915_gem_object_unset_pages() + * called for obj3 => TLB flush + * invalidating both obj1 and obj2. + * seqno += 2 + * seqno=4 + * unbind/evict event + * obj2.mm.tlb = seqno | 1 + * __i915_gem_object_unset_pages() + * called for obj1, don't flush, + * as past flush invalidated obj1 + * + * __i915_gem_object_unset_pages() + * called for obj2 => TLB flush + * seqno += 2 + * seqno=6 + */ + void intel_gt_invalidate_tlb_full(struct intel_gt *gt, u32 seqno); void intel_gt_init_tlb(struct intel_gt *gt); void intel_gt_fini_tlb(struct intel_gt *gt); +/** + * intel_gt_tlb_seqno - Returns the current TLB invlidation sequence number + * + * @gt: GT structure + * + * There's no need to lock while calling it, as seqprop_sequence is thread-safe + */ static inline u32 intel_gt_tlb_seqno(const struct intel_gt *gt) { return seqprop_sequence(>->tlb.seqno); } +/** + * intel_gt_next_invalidate_tlb_full - Returns the next TLB full invalidation + * sequence number + * + * @gt: GT structure + * + * There's no need to lock while calling it, as seqprop_sequence is thread-safe + */ static inline u32 intel_gt_next_invalidate_tlb_full(const struct intel_gt *gt) { return intel_gt_tlb_seqno(gt) | 1; -- 2.36.1
