On Tue, 2 Aug 2022 15:30:44 -0700 Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx> wrote: > On Fri, Jul 29, 2022 at 09:03:55AM +0200, Mauro Carvalho Chehab wrote: > >Add a description for the TLB cache invalidation algorithm and for > >the related kAPI functions. > > > >Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > >--- > > > >To avoid mailbombing on a large number of people, only mailing lists were C/C on the cover. > >See [PATCH v2 0/2] at: https://lore.kernel.org/all/cover.1659077372.git.mchehab@xxxxxxxxxx/ > > > > Documentation/gpu/i915.rst | 7 ++ > > drivers/gpu/drm/i915/gt/intel_tlb.c | 25 +++++++ > > drivers/gpu/drm/i915/gt/intel_tlb.h | 101 ++++++++++++++++++++++++++++ > > 3 files changed, 133 insertions(+) > > > >diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst > >index 4e59db1cfb00..46911fdd79e8 100644 > >--- a/Documentation/gpu/i915.rst > >+++ b/Documentation/gpu/i915.rst > >@@ -58,6 +58,13 @@ Intel GVT-g Host Support(vGPU device model) > > .. kernel-doc:: drivers/gpu/drm/i915/intel_gvt.c > > :internal: > > > >+TLB cache invalidation > >+---------------------- > >+ > >+.. kernel-doc:: drivers/gpu/drm/i915/gt/intel_tlb.h > >+ > >+.. kernel-doc:: drivers/gpu/drm/i915/gt/intel_tlb.c > >+ > > Workarounds > > ----------- > > > >diff --git a/drivers/gpu/drm/i915/gt/intel_tlb.c b/drivers/gpu/drm/i915/gt/intel_tlb.c > >index af8cae979489..4873b7ecc015 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 MMIO-based TLB flush for GEN8 to GEN12. > >+ */ > > 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 > > Free TLB-specific vars OK. > > >+ * @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..dca70c33bd61 100644 > >--- a/drivers/gpu/drm/i915/gt/intel_tlb.h > >+++ b/drivers/gpu/drm/i915/gt/intel_tlb.h > >@@ -11,16 +11,117 @@ > > > > #include "intel_gt_types.h" > > > >+/** > >+ * DOC: TLB cache invalidation logic > >+ * > >+ * The way the current algorithm works is that a struct 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, a sequence number provided by > >+ * intel_gt_next_invalidate_tlb_full() is stored on it. 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_full() is called, > >+ * where it checks if the sequence number of the object was already invalidated > >+ * or not. If not, it flushes the TLB and increments the sequence number:: > >+ * > >+ * void intel_gt_invalidate_tlb_full(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; > >+ * > >+ * // Some code to do TLB invalidation > >+ * ... > >+ * > >+ * write_seqcount_invalidate(>->tlb.seqno); // increment seqno > >+ * mutex_lock(>->tlb.invalidate_lock); > >+ * } > >+ * > >+ * 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. > > I am trying to get my head around the below function. > > void vma_invalidate_tlb(struct i915_address_space *vm, u32 tlb) > { > WRITE_ONCE(tlb, intel_gt_next_invalidate_tlb_full(vm->gt)); > } > > Though we pass obj->mm.tlb for 'tlb' while calling this function, > aren't we writing to local 'tlb' variable here instead of obj->mm.tlb? It should be passing a pointer. I wrote such fix after a review, but somehow it ended getting lost. I'll send the fix at v3. > >+ * > >+ * Different threads may be used on unbind/evict and/or unset pages. > >+ * As the logic at void intel_gt_invalidate_tlb_full() is protected by a mutex, > > May be we can skip 'void' and just keep function name here. Sure. > >+ * for simplicity, let's consider just two threads: > >+ * > >+ * +-------------------+-------------------------+---------------------------------+ > >+ * | sequence number | Thread 0 | Thread 1 + > >+ * +===================+=========================+=================================+ > >+ * | seqno=2 | | | > >+ * | +-------------------------+---------------------------------+ > >+ * | | unbind/evict obj3. | | > >+ * | | | | > >+ * | | obj3.mm.tlb = seqno | 1 | | > >+ * | | // obj3.mm.tlb = 3 | | > >+ * | +-------------------------+---------------------------------+ > >+ * | | unbind/evict obj1. | | > >+ * | | | | > >+ * | | obj1.mm.tlb = seqno | 1 | | > >+ * | | // obj1.mm.tlb = 3 | | > >+ * | +-------------------------+---------------------------------+ > >+ * | | | __i915_gem_object_unset_pages() | > >+ * | | | called for obj3 => TLB flush | > >+ * | | | invalidating both obj1 and obj2.| > >+ * | | | | > >+ * | | | seqno += 2 | > >+ * +-------------------+-------------------------+---------------------------------+ > >+ * | seqno=4 | | | > >+ * | +-------------------------+---------------------------------+ > >+ * | | unbind/evict obj2. | | > >+ * | | | | > >+ * | | obj2.mm.tlb = seqno | 1 | | > >+ * | | // obj2.mm.tlb = 5 | | > >+ * | +-------------------------+---------------------------------+ > >+ * | | | __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. | > >+ * | | | invalidating obj2. | > >+ * | | | | > >+ * | | | 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 > >+ * > > Probably this empty comment line needs to be removed before the parameter > description below? Kernel-doc actually accepts both with or without a blank line. My personal preference is to place a blank line, because sometimes the function description plus function name is bigger than one line. So, it is usually clearer when adding a blank line than doing something like this (perfectly valid kerneldoc markup): /** * long_function_name_foo - Lorem ipsum dolor sit amet, consectetur * adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore. * @bar: some parameter * ... But yeah, kernel-doc documentation example doesn't have a blank line. So, I'll drop it. > > >+ * @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 > >+ * > > Same here. > > -Niranjana > > >+ * @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 > > Thanks! Mauro
