Re: [Intel-gfx] [PATCH 18/23] drm/i915: Keep all partially allocated HWSP on a freelist

[Mika Kuoppala]

Chris Wilson <ch...@chris-wilson.co.uk> writes:

> Keep track of partially allocated pages for use in allocating future
> timeline HWSP. This is still without migration, so it is possible for

timeline from HWSP?

> the system to end up with each timeline in its own page, but we ensure
> that no new allocation would needless allocate a fresh page!

s/needless/needlessly.
-Mika

>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: John Harrison <john.c.harri...@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |  3 +-
>  drivers/gpu/drm/i915/i915_timeline.c | 81 +++++++++++++++++-----------
>  2 files changed, 50 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index d59228dabb6e..0bebef428f1e 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1981,8 +1981,7 @@ struct drm_i915_private {
>  
>                       /* Pack multiple timelines' seqnos into the same page */
>                       spinlock_t hwsp_lock;
> -                     struct i915_vma *hwsp;
> -                     u64 bitmap;
> +                     struct list_head hwsp;
>               } timelines;
>  
>               struct list_head active_rings;
> diff --git a/drivers/gpu/drm/i915/i915_timeline.c 
> b/drivers/gpu/drm/i915/i915_timeline.c
> index e939a9e1a4ab..64bb1ce24318 100644
> --- a/drivers/gpu/drm/i915/i915_timeline.c
> +++ b/drivers/gpu/drm/i915/i915_timeline.c
> @@ -9,74 +9,94 @@
>  #include "i915_timeline.h"
>  #include "i915_syncmap.h"
>  
> +struct i915_timeline_hwsp {
> +     struct list_head link;
> +     struct i915_vma *vma;
> +     u64 bitmap;
> +};
> +
>  static int hwsp_alloc(struct i915_timeline *timeline)
>  {
> -#define NBITS BITS_PER_TYPE(typeof(gt->bitmap))
>       struct drm_i915_private *i915 = timeline->i915;
>       struct i915_gt_timelines *gt = &i915->gt.timelines;
> -     struct i915_vma *vma;
> +     struct i915_timeline_hwsp *hwsp;
>       int offset;
>  
>       spin_lock(&gt->hwsp_lock);
>  
> -restart:
> -     offset = find_first_bit((unsigned long *)&gt->bitmap, NBITS);
> -     if (offset == NBITS && gt->hwsp) {
> -             i915_vma_put(gt->hwsp);
> -             gt->hwsp = NULL;
> -     }
> -
> -     vma = gt->hwsp;
> -     if (!vma) {
> +     hwsp = list_first_entry_or_null(&gt->hwsp, typeof(*hwsp), link);
> +     if (!hwsp) {
>               struct drm_i915_gem_object *bo;
> +             struct i915_vma *vma;
>  
>               spin_unlock(&gt->hwsp_lock);
>  
> -             BUILD_BUG_ON(NBITS * CACHELINE_BYTES > PAGE_SIZE);
> +             hwsp = kmalloc(sizeof(*hwsp), GFP_KERNEL);
> +             if (!hwsp)
> +                     return -ENOMEM;
> +
> +             BUILD_BUG_ON(BITS_PER_TYPE(hwsp->bitmap) * CACHELINE_BYTES > 
> PAGE_SIZE);
>               bo = i915_gem_object_create_internal(i915, PAGE_SIZE);
> -             if (IS_ERR(bo))
> +             if (IS_ERR(bo)) {
> +                     kfree(hwsp);
>                       return PTR_ERR(bo);
> +             }
>  
>               i915_gem_object_set_cache_level(bo, I915_CACHE_LLC);
>  
>               vma = i915_vma_instance(bo, &i915->ggtt.vm, NULL);
>               if (IS_ERR(vma)) {
>                       i915_gem_object_put(bo);
> +                     kfree(hwsp);
>                       return PTR_ERR(vma);
>               }
>  
> -             spin_lock(&gt->hwsp_lock);
> -             if (gt->hwsp) {
> -                     i915_gem_object_put(bo);
> -                     goto restart;
> -             }
> +             vma->private = hwsp;
> +             hwsp->vma = vma;
> +             hwsp->bitmap = ~0ull;
>  
> -             gt->hwsp = vma;
> -             gt->bitmap = ~0ull;
> -             offset = 0;
> +             spin_lock(&gt->hwsp_lock);
> +             list_add(&hwsp->link, &gt->hwsp);
>       }
>  
> -     gt->bitmap &= ~BIT_ULL(offset);
> +     GEM_BUG_ON(!hwsp->bitmap);
> +     offset = __ffs64(hwsp->bitmap);
> +     hwsp->bitmap &= ~BIT_ULL(offset);
> +     if (!hwsp->bitmap)
> +             list_del(&hwsp->link);
>  
>       spin_unlock(&gt->hwsp_lock);
>  
> -     timeline->hwsp_ggtt = i915_vma_get(vma);
> +     timeline->hwsp_ggtt = i915_vma_get(hwsp->vma);
>       timeline->hwsp_offset = offset * CACHELINE_BYTES;
>  
> +     GEM_BUG_ON(timeline->hwsp_ggtt->private != hwsp);
> +
>       return 0;
> -#undef NBITS
>  }
>  
>  static void hwsp_free(struct i915_timeline *timeline)
>  {
>       struct i915_gt_timelines *gt = &timeline->i915->gt.timelines;
> +     struct i915_timeline_hwsp *hwsp;
>  
> -     if (timeline->hwsp_ggtt != gt->hwsp)
> +     hwsp = timeline->hwsp_ggtt->private;
> +     if (!hwsp)
>               return;
>  
>       spin_lock(&gt->hwsp_lock);
> -     if (timeline->hwsp_ggtt == gt->hwsp)
> -             gt->bitmap |= BIT_ULL(timeline->hwsp_offset / CACHELINE_BYTES);
> +
> +     if (!hwsp->bitmap)
> +             list_add_tail(&hwsp->link, &gt->hwsp);
> +
> +     hwsp->bitmap |= BIT_ULL(timeline->hwsp_offset / CACHELINE_BYTES);
> +
> +     if (hwsp->bitmap == ~0ull) {
> +             i915_vma_put(hwsp->vma);
> +             list_del(&hwsp->link);
> +             kfree(hwsp);
> +     }
> +
>       spin_unlock(&gt->hwsp_lock);
>  }
>  
> @@ -148,6 +168,7 @@ void i915_timelines_init(struct drm_i915_private *i915)
>       INIT_LIST_HEAD(&gt->list);
>  
>       spin_lock_init(&gt->hwsp_lock);
> +     INIT_LIST_HEAD(&gt->hwsp);
>  
>       /* via i915_gem_wait_for_idle() */
>       i915_gem_shrinker_taints_mutex(i915, &gt->mutex);
> @@ -264,13 +285,9 @@ void __i915_timeline_free(struct kref *kref)
>  void i915_timelines_fini(struct drm_i915_private *i915)
>  {
>       struct i915_gt_timelines *gt = &i915->gt.timelines;
> -     struct i915_vma *vma;
>  
>       GEM_BUG_ON(!list_empty(&gt->list));
> -
> -     vma = fetch_and_zero(&i915->gt.timelines.hwsp);
> -     if (vma)
> -             i915_vma_put(vma);
> +     GEM_BUG_ON(!list_empty(&gt->hwsp));
>  
>       mutex_destroy(&gt->mutex);
>  }
> -- 
> 2.20.1
>
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