[Mesa-dev] [PATCH 2/2] winsys/amdgpu: explicitly declare whether buffer_map is permanent or not
Nicolai Hähnle
nhaehnle at gmail.com
Thu Nov 22 11:24:06 UTC 2018
On 21.11.18 21:27, Marek Olšák wrote:
> On Wed, Nov 21, 2018 at 12:57 PM Nicolai Hähnle <nhaehnle at gmail.com
> <mailto:nhaehnle at gmail.com>> wrote:
>
> From: Nicolai Hähnle <nicolai.haehnle at amd.com
> <mailto:nicolai.haehnle at amd.com>>
>
> Introduce a new driver-private transfer flag RADEON_TRANSFER_TEMPORARY
> that specifies whether the caller will use buffer_unmap or not. The
> default behavior is set to permanent maps, because that's what drivers
> do for Gallium buffer maps.
>
> This should eliminate the need for hacks in libdrm. Assertions are added
> to catch when the buffer_unmap calls don't match the (temporary)
> buffer_map calls.
>
> I did my best to update r600 and r300 as well for completeness (yes,
> it's a no-op for r300 because it never calls buffer_unmap), even though
> the radeon winsys ignores the new flag.
>
>
> You didn't make any changes to r300.
Yeah, that's what I wrote :)
> You can also drop all r600 changes, because the radeon winsys doesn't care.
I don't think it's a good idea, though. The interface of the two winsys
is different, yes, but it's largely the same and it makes sense to keep
it that way conceptually. Not that it matters much for the code itself.
[snip]
> +enum radeon_transfer_flags {
> + /* Indicates that the caller will unmap the buffer.
> + *
> + * Not unmapping buffers is an important performance
> optimization for
> + * OpenGL (avoids kernel overhead for frequently mapped
> buffers). However,
> + * if you only map a buffer once and then use it indefinitely
> from the GPU,
> + * it is much better to unmap it so that the kernel is free to
> move it to
> + * non-visible VRAM.
>
>
> The second half of the comment is misleading. The kernel will move
> buffers to invisible VRAM regardless of whether they're mapped, so CPU
> mappings have no effect on the placement. Buffers are only moved back to
> CPU-accessible memory on a CPU page fault. If a buffer is mapped and
> there no CPU access, it will stay in invisible VRAM forever. The general
> recommendation is to keep those buffers mapped for CPU access just like
> GTT buffers.
Yeah, I'll change that.
> + */
> + RADEON_TRANSFER_TEMPORARY = (PIPE_TRANSFER_DRV_PRV << 0),
> +};
> +
> #define RADEON_SPARSE_PAGE_SIZE (64 * 1024)
>
> enum ring_type {
> RING_GFX = 0,
> RING_COMPUTE,
> RING_DMA,
> RING_UVD,
> RING_VCE,
> RING_UVD_ENC,
> RING_VCN_DEC,
> @@ -287,23 +299,26 @@ struct radeon_winsys {
> struct pb_buffer *(*buffer_create)(struct radeon_winsys *ws,
> uint64_t size,
> unsigned alignment,
> enum radeon_bo_domain domain,
> enum radeon_bo_flag flags);
>
> /**
> * Map the entire data store of a buffer object into the
> client's address
> * space.
> *
> + * Callers are expected to unmap buffers again if and only if the
> + * RADEON_TRANSFER_TEMPORARY flag is set in \p usage.
> + *
> * \param buf A winsys buffer object to map.
> * \param cs A command stream to flush if the buffer is
> referenced by it.
> - * \param usage A bitmask of the PIPE_TRANSFER_* flags.
> + * \param usage A bitmask of the PIPE_TRANSFER_* and
> RADEON_TRANSFER_* flags.
> * \return The pointer at the beginning of the buffer.
> */
> void *(*buffer_map)(struct pb_buffer *buf,
> struct radeon_cmdbuf *cs,
> enum pipe_transfer_usage usage);
>
> /**
> * Unmap a buffer object from the client's address space.
> *
> * \param buf A winsys buffer object to unmap.
> diff --git a/src/gallium/drivers/radeonsi/si_shader.c
> b/src/gallium/drivers/radeonsi/si_shader.c
> index 19522cc97b1..d455fb5db6a 100644
> --- a/src/gallium/drivers/radeonsi/si_shader.c
> +++ b/src/gallium/drivers/radeonsi/si_shader.c
> @@ -5286,21 +5286,22 @@ int si_shader_binary_upload(struct si_screen
> *sscreen, struct si_shader *shader)
> 0 :
> SI_RESOURCE_FLAG_READ_ONLY,
> PIPE_USAGE_IMMUTABLE,
> align(bo_size,
> SI_CPDMA_ALIGNMENT),
> 256);
> if (!shader->bo)
> return -ENOMEM;
>
> /* Upload. */
> ptr = sscreen->ws->buffer_map(shader->bo->buf, NULL,
> PIPE_TRANSFER_READ_WRITE |
> - PIPE_TRANSFER_UNSYNCHRONIZED);
> + PIPE_TRANSFER_UNSYNCHRONIZED |
> + RADEON_TRANSFER_TEMPORARY);
>
> /* Don't use util_memcpy_cpu_to_le32. LLVM binaries are
> * endian-independent. */
> if (prolog) {
> memcpy(ptr, prolog->code, prolog->code_size);
> ptr += prolog->code_size;
> }
> if (previous_stage) {
> memcpy(ptr, previous_stage->code,
> previous_stage->code_size);
> ptr += previous_stage->code_size;
> diff --git a/src/gallium/include/pipe/p_defines.h
> b/src/gallium/include/pipe/p_defines.h
> index 693f041b1da..e99895d30d8 100644
> --- a/src/gallium/include/pipe/p_defines.h
> +++ b/src/gallium/include/pipe/p_defines.h
> @@ -334,21 +334,27 @@ enum pipe_transfer_usage
> */
> PIPE_TRANSFER_PERSISTENT = (1 << 13),
>
> /**
> * If PERSISTENT is set, this ensures any writes done by the
> device are
> * immediately visible to the CPU and vice versa.
> *
> * PIPE_RESOURCE_FLAG_MAP_COHERENT must be set when creating
> * the resource.
> */
> - PIPE_TRANSFER_COHERENT = (1 << 14)
> + PIPE_TRANSFER_COHERENT = (1 << 14),
> +
> + /**
> + * This and higher bits are reserved for private use by drivers.
> Drivers
> + * should use this as (PIPE_TRANSFER_DRV_PRV << i).
> + */
> + PIPE_TRANSFER_DRV_PRV = (1 << 24)
> };
>
> /**
> * Flags for the flush function.
> */
> enum pipe_flush_flags
> {
> PIPE_FLUSH_END_OF_FRAME = (1 << 0),
> PIPE_FLUSH_DEFERRED = (1 << 1),
> PIPE_FLUSH_FENCE_FD = (1 << 2),
> diff --git a/src/gallium/winsys/amdgpu/drm/amdgpu_bo.c
> b/src/gallium/winsys/amdgpu/drm/amdgpu_bo.c
> index 9f0d4c12482..355018c76fc 100644
> --- a/src/gallium/winsys/amdgpu/drm/amdgpu_bo.c
> +++ b/src/gallium/winsys/amdgpu/drm/amdgpu_bo.c
> @@ -49,20 +49,21 @@
> struct amdgpu_sparse_backing_chunk {
> uint32_t begin, end;
> };
>
> static struct pb_buffer *
> amdgpu_bo_create(struct radeon_winsys *rws,
> uint64_t size,
> unsigned alignment,
> enum radeon_bo_domain domain,
> enum radeon_bo_flag flags);
> +static void amdgpu_bo_unmap(struct pb_buffer *buf);
>
> static bool amdgpu_bo_wait(struct pb_buffer *_buf, uint64_t timeout,
> enum radeon_bo_usage usage)
> {
> struct amdgpu_winsys_bo *bo = amdgpu_winsys_bo(_buf);
> struct amdgpu_winsys *ws = bo->ws;
> int64_t abs_timeout;
>
> if (timeout == 0) {
> if (p_atomic_read(&bo->num_active_ioctls))
> @@ -166,20 +167,26 @@ static void amdgpu_bo_remove_fences(struct
> amdgpu_winsys_bo *bo)
> bo->max_fences = 0;
> }
>
> void amdgpu_bo_destroy(struct pb_buffer *_buf)
> {
> struct amdgpu_winsys_bo *bo = amdgpu_winsys_bo(_buf);
> struct amdgpu_winsys *ws = bo->ws;
>
> assert(bo->bo && "must not be called for slab entries");
>
> + if (!bo->is_user_ptr && bo->cpu_ptr) {
> + bo->cpu_ptr = NULL;
> + amdgpu_bo_unmap(&bo->base);
> + }
> + assert(bo->is_user_ptr || bo->u.real.map_count == 0);
> +
> if (ws->debug_all_bos) {
> simple_mtx_lock(&ws->global_bo_list_lock);
> LIST_DEL(&bo->u.real.global_list_item);
> ws->num_buffers--;
> simple_mtx_unlock(&ws->global_bo_list_lock);
> }
>
> simple_mtx_lock(&ws->bo_export_table_lock);
> util_hash_table_remove(ws->bo_export_table, bo->bo);
> simple_mtx_unlock(&ws->bo_export_table_lock);
> @@ -188,54 +195,66 @@ void amdgpu_bo_destroy(struct pb_buffer *_buf)
> amdgpu_va_range_free(bo->u.real.va_handle);
> amdgpu_bo_free(bo->bo);
>
> amdgpu_bo_remove_fences(bo);
>
> if (bo->initial_domain & RADEON_DOMAIN_VRAM)
> ws->allocated_vram -= align64(bo->base.size,
> ws->info.gart_page_size);
> else if (bo->initial_domain & RADEON_DOMAIN_GTT)
> ws->allocated_gtt -= align64(bo->base.size,
> ws->info.gart_page_size);
>
> - if (bo->u.real.map_count >= 1) {
> - if (bo->initial_domain & RADEON_DOMAIN_VRAM)
> - ws->mapped_vram -= bo->base.size;
> - else if (bo->initial_domain & RADEON_DOMAIN_GTT)
> - ws->mapped_gtt -= bo->base.size;
> - ws->num_mapped_buffers--;
> - }
> -
> simple_mtx_destroy(&bo->lock);
> FREE(bo);
> }
>
> static void amdgpu_bo_destroy_or_cache(struct pb_buffer *_buf)
> {
> struct amdgpu_winsys_bo *bo = amdgpu_winsys_bo(_buf);
>
> assert(bo->bo); /* slab buffers have a separate vtbl */
>
> if (bo->u.real.use_reusable_pool)
> pb_cache_add_buffer(&bo->u.real.cache_entry);
> else
> amdgpu_bo_destroy(_buf);
> }
>
> +static bool amdgpu_bo_do_map(struct amdgpu_winsys_bo *bo, void **cpu)
> +{
> + assert(!bo->sparse && bo->bo && !bo->is_user_ptr);
> + int r = amdgpu_bo_cpu_map(bo->bo, cpu);
> + if (r) {
> + /* Clear the cache and try again. */
> + pb_cache_release_all_buffers(&bo->ws->bo_cache);
> + r = amdgpu_bo_cpu_map(bo->bo, cpu);
> + if (r)
> + return false;
> + }
> +
> + if (p_atomic_inc_return(&bo->u.real.map_count) == 1) {
> + if (bo->initial_domain & RADEON_DOMAIN_VRAM)
> + bo->ws->mapped_vram += bo->base.size;
> + else if (bo->initial_domain & RADEON_DOMAIN_GTT)
> + bo->ws->mapped_gtt += bo->base.size;
> + bo->ws->num_mapped_buffers++;
> + }
> +
> + return true;
> +}
> +
> static void *amdgpu_bo_map(struct pb_buffer *buf,
> struct radeon_cmdbuf *rcs,
> enum pipe_transfer_usage usage)
> {
> struct amdgpu_winsys_bo *bo = (struct amdgpu_winsys_bo*)buf;
> struct amdgpu_winsys_bo *real;
> struct amdgpu_cs *cs = (struct amdgpu_cs*)rcs;
> - int r;
> - void *cpu = NULL;
> - uint64_t offset = 0;
>
> assert(!bo->sparse);
>
> /* If it's not unsynchronized bo_map, flush CS if needed and
> then wait. */
> if (!(usage & PIPE_TRANSFER_UNSYNCHRONIZED)) {
> /* DONTBLOCK doesn't make sense with UNSYNCHRONIZED. */
> if (usage & PIPE_TRANSFER_DONTBLOCK) {
> if (!(usage & PIPE_TRANSFER_WRITE)) {
> /* Mapping for read.
> *
> @@ -306,63 +325,74 @@ static void *amdgpu_bo_map(struct pb_buffer *buf,
> }
>
> amdgpu_bo_wait((struct pb_buffer*)bo,
> PIPE_TIMEOUT_INFINITE,
> RADEON_USAGE_READWRITE);
> }
>
> bo->ws->buffer_wait_time += os_time_get_nano() - time;
> }
> }
>
> - /* If the buffer is created from user memory, return the user
> pointer. */
> - if (bo->user_ptr)
> - return bo->user_ptr;
> + /* Buffer synchronization has been checked, now actually map the
> buffer. */
> + void *cpu = NULL;
> + uint64_t offset = 0;
>
> if (bo->bo) {
> real = bo;
> } else {
> real = bo->u.slab.real;
> offset = bo->va - real->va;
> }
>
> - r = amdgpu_bo_cpu_map(real->bo, &cpu);
> - if (r) {
> - /* Clear the cache and try again. */
> - pb_cache_release_all_buffers(&real->ws->bo_cache);
> - r = amdgpu_bo_cpu_map(real->bo, &cpu);
> - if (r)
> - return NULL;
> + if (usage & RADEON_TRANSFER_TEMPORARY) {
> + if (real->is_user_ptr) {
> + cpu = real->cpu_ptr;
> + } else {
> + if (!amdgpu_bo_do_map(real, &cpu))
> + return NULL;
> + }
> + } else {
> + cpu = real->cpu_ptr;
> + if (!cpu) {
>
>
> I think this is unsafe on 64-bit CPUs, because the lower 32 bits can be
> initialized but not the upper 32 bits. You would either have to check
> both 32-bit halves separately (if they are both expected to be non-zero)
> or you would have to lock the mutex first.
Well, there is actually a potential problem, but it's not that. A 64-bit
CPU will do aligned 64-bit loads/stores atomically, but
amdgpu_bo_cpu_map doesn't necessarily guarantee that it'll set the
address atomically. I think it does that today, but it's a bad idea to
depend on it.
> If all my remarks are addressed, I'll ack this, but I still think that
> this patch adds unnecessary cruft, complexity, and fragility in order to
> fix an issue that is very trivial in nature. The overflow check in
> libdrm is simple, clean, and robust.
The overflow check, or actually the saturating behavior, is also very
surprising and unusual. Reference counting doesn't usually work that way.
Cheers,
Nicolai
--
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.
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