Re: [Intel-gfx] [PATCH v2 2/2] drm/i915/gt: document TLB cache invalidation functions
On Tue, 2 Aug 2022 15:30:44 -0700
Niranjana Vishwanathapura 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
> >---
> >
> >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.mche...@kernel.org/
> >
> > 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 g
Re: [Intel-gfx] [PATCH v2 2/2] drm/i915/gt: document TLB cache invalidation functions
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
---
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.mche...@kernel.org/
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
+ * @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?
+ *
+ * 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
