[Mesa-dev] [PATCH v3 2/6] anv: Add a helper for doing mass allocations

[Jason Ekstrand]

On Fri, Apr 7, 2017 at 1:26 PM, Chris Wilson <chris at chris-wilson.co.uk>
wrote:

> On Fri, Apr 07, 2017 at 12:55:53PM -0700, Jason Ekstrand wrote:
> > We tend to try to reduce the number of allocation calls the Vulkan
> > driver uses by doing a single allocation whenever possible for a data
> > structure.  While this has certain downsides (usually code complexity),
> > it does mean error handling and cleanup is much easier.  This commit
> > adds a nice little helper struct for getting rid of some of that
> > complexity.
> > ---
> >  src/intel/vulkan/anv_private.h | 77 ++++++++++++++++++++++++++++++
> ++++++++++++
> >  1 file changed, 77 insertions(+)
> >
> > diff --git a/src/intel/vulkan/anv_private.h b/src/intel/vulkan/anv_
> private.h
> > index 90974d9..f941cc7 100644
> > --- a/src/intel/vulkan/anv_private.h
> > +++ b/src/intel/vulkan/anv_private.h
> > @@ -269,6 +269,83 @@ void anv_loge_v(const char *format, va_list va);
> >  #define anv_assert(x)
> >  #endif
> >
> > +struct anv_multialloc {
> > +    size_t size;
> > +    size_t align;
> > +
> > +    uint32_t ptr_count;
> > +    void **ptrs[8];
> > +};
> > +
> > +#define ANV_MULTIALLOC_INIT \
> > +   ((struct anv_multialloc) { 0, })
> > +
> > +#define ANV_MULTIALLOC(_name) \
> > +   struct anv_multialloc _name = ANV_MULTIALLOC_INIT
> > +
> > +static inline void
> > +_anv_multialloc_add(struct anv_multialloc *ma,
> > +                    void **ptr, size_t size, size_t align)
> > +{
> > +   size_t offset = align_u64(ma->size, align);
> > +   ma->size = offset + size;
> > +   ma->align = MAX2(ma->align, align);
> > +
> > +   /* Store the offset in the pointer. */
> > +   *ptr = (void *)(uintptr_t)offset;
> > +
> > +   assert(ma->ptr_count < ARRAY_SIZE(ma->ptrs));
> > +   ma->ptrs[ma->ptr_count++] = ptr;
> > +}
> > +
> > +#define anv_multialloc_add(_ma, _ptr, _count) \
> > +   _anv_multialloc_add((_ma), (void **)(_ptr), \
> > +                       (_count) * sizeof(**(_ptr)),
> __alignof__(**(_ptr)))
> > +
> > +static inline void *
> > +anv_multialloc_alloc(struct anv_multialloc *ma,
> > +                     const VkAllocationCallbacks *alloc,
> > +                     VkSystemAllocationScope scope)
> > +{
> > +   void *ptr = vk_alloc(alloc, ma->size, ma->align, scope);
> > +   if (!ptr)
> > +      return NULL;
> > +
> > +   /* Fill out each of the pointers with their final value.
> > +    *
> > +    *   for (uint32_t i = 0; i < ma->ptr_count; i++)
> > +    *      *ma->ptrs[i] = ptr + (uintptr_t)*ma->ptrs[i];
> > +    *
> > +    * Unfortunately, even though ma->ptr_count is basically guaranteed
> to be a
> > +    * constant, GCC is incapable of figuring this out and unrolling the
> loop
> > +    * so we have to give it a little help.
> > +    */
> > +   STATIC_ASSERT(ARRAY_SIZE(ma->ptrs) == 8);
> > +#define _ANV_MULTIALLOC_UPDATE_POINTER(_i) \
> > +   if ((_i) < ma->ptr_count) \
> > +      *ma->ptrs[_i] = ptr + (uintptr_t)*ma->ptrs[_i]
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(0);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(1);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(2);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(3);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(4);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(5);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(6);
> > +   _ANV_MULTIALLOC_UPDATE_POINTER(7);
> > +#undef _ANV_MULTIALLOC_UPDATE_POINTER
>
> #define _ANV_MULTIALLOC_UPDATE_POINTER(_i) case _i + 1: *ma->ptrs[_i] =
> ptr +(uintptr)*ma->ptrs[_i]
>
> switch (ma->ptr_count) {
> _ANV_MULTIALLOC_UPDATE_POINTER(7);
> _ANV_MULTIALLOC_UPDATE_POINTER(6);
> _ANV_MULTIALLOC_UPDATE_POINTER(5);
> _ANV_MULTIALLOC_UPDATE_POINTER(4);
> _ANV_MULTIALLOC_UPDATE_POINTER(3);
> _ANV_MULTIALLOC_UPDATE_POINTER(2);
> _ANV_MULTIALLOC_UPDATE_POINTER(1);
> _ANV_MULTIALLOC_UPDATE_POINTER(0);
> }
>
> #undef _ANV_MULITALLOC_UPDATE_POINTER
>

If ma->ptr_count is constant, they generate exactly the same code.  If it
isn't (i.e. if one of the multialloc_adds is predicated), then they still
generate basically the same code with the code for the if version being
slightly more straightforward.
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