[Mesa-dev] [PATCH 7/7] st/mesa: cache staging texture for glReadPixels
Marek Olšák
maraeo at gmail.com
Mon Jun 20 13:31:35 UTC 2016
For the series:
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
Marek
On Wed, Jun 15, 2016 at 10:38 AM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>
> ---
> src/mesa/state_tracker/st_cb_fbo.h | 2 +
> src/mesa/state_tracker/st_cb_readpixels.c | 122 ++++++++++++++++++++++++++----
> 2 files changed, 110 insertions(+), 14 deletions(-)
>
> diff --git a/src/mesa/state_tracker/st_cb_fbo.h b/src/mesa/state_tracker/st_cb_fbo.h
> index f3b310b..414a661 100644
> --- a/src/mesa/state_tracker/st_cb_fbo.h
> +++ b/src/mesa/state_tracker/st_cb_fbo.h
> @@ -58,6 +58,8 @@ struct st_renderbuffer
> boolean software;
> void *data;
>
> + bool use_readpix_cache;
> +
> /* Inputs from Driver.RenderTexture, don't use directly. */
> boolean is_rtt; /**< whether Driver.RenderTexture was called */
> unsigned rtt_face, rtt_slice;
> diff --git a/src/mesa/state_tracker/st_cb_readpixels.c b/src/mesa/state_tracker/st_cb_readpixels.c
> index a501b7b..42d147f 100644
> --- a/src/mesa/state_tracker/st_cb_readpixels.c
> +++ b/src/mesa/state_tracker/st_cb_readpixels.c
> @@ -46,6 +46,28 @@
> #include "state_tracker/st_pbo.h"
> #include "state_tracker/st_texture.h"
>
> +/* The readpixels cache caches a blitted staging texture so that back-to-back
> + * calls to glReadPixels with user pointers require less CPU-GPU synchronization.
> + *
> + * Assumptions:
> + *
> + * (1) Blits have high synchronization overheads, and it is beneficial to
> + * use a single blit of the entire framebuffer instead of many smaller
> + * blits (because the smaller blits cannot be batched, and we have to wait
> + * for the GPU after each one).
> + *
> + * (2) transfer_map implicitly involves a blit as well (for de-tiling, copy
> + * from VRAM, etc.), so that it is beneficial to replace the
> + * _mesa_readpixels path as well when possible.
> + *
> + */
> +#define USE_READPIXELS_CACHE true
> +
> +/* Fill and use the cache whenever possible (inefficient; only meant for
> + * testing / debugging).
> + */
> +#define ALWAYS_READPIXELS_CACHE false
> +
> static boolean
> needs_integer_signed_unsigned_conversion(const struct gl_context *ctx,
> GLenum format, GLenum type)
> @@ -299,6 +321,62 @@ blit_to_staging(struct st_context *st, struct st_renderbuffer *strb,
> return dst;
> }
>
> +static struct pipe_resource *
> +try_cached_readpixels(struct st_context *st, struct st_renderbuffer *strb,
> + bool invert_y,
> + GLsizei width, GLsizei height,
> + GLenum format,
> + enum pipe_format src_format, enum pipe_format dst_format)
> +{
> + struct pipe_resource *src = strb->texture;
> + struct pipe_resource *dst = NULL;
> +
> + if (!USE_READPIXELS_CACHE)
> + return NULL;
> +
> + /* Reset cache after invalidation or switch of parameters. */
> + if (st->readpix_cache.src != src ||
> + st->readpix_cache.dst_format != dst_format ||
> + st->readpix_cache.level != strb->surface->u.tex.level ||
> + st->readpix_cache.layer != strb->surface->u.tex.first_layer) {
> + pipe_resource_reference(&st->readpix_cache.src, src);
> + pipe_resource_reference(&st->readpix_cache.cache, NULL);
> + st->readpix_cache.dst_format = dst_format;
> + st->readpix_cache.level = strb->surface->u.tex.level;
> + st->readpix_cache.layer = strb->surface->u.tex.first_layer;
> + st->readpix_cache.hits = 0;
> + }
> +
> + /* Decide whether to trigger the cache. */
> + if (!st->readpix_cache.cache) {
> + if (!strb->use_readpix_cache && !ALWAYS_READPIXELS_CACHE) {
> + /* Heuristic: If previous successive calls read at least a fraction
> + * of the surface _and_ we read again, trigger the cache.
> + */
> + unsigned threshold = MAX2(1, strb->Base.Width * strb->Base.Height / 8);
> +
> + if (st->readpix_cache.hits < threshold) {
> + st->readpix_cache.hits += width * height;
> + return NULL;
> + }
> +
> + strb->use_readpix_cache = true;
> + }
> +
> + /* Fill the cache */
> + st->readpix_cache.cache = blit_to_staging(st, strb, invert_y,
> + 0, 0,
> + strb->Base.Width,
> + strb->Base.Height, format,
> + src_format, dst_format);
> + }
> +
> + /* Return an owning reference to stay consistent with the non-cached path */
> + pipe_resource_reference(&dst, st->readpix_cache.cache);
> +
> + return dst;
> +}
> +
> /**
> * This uses a blit to copy the read buffer to a texture format which matches
> * the format and type combo and then a fast read-back is done using memcpy.
> @@ -330,6 +408,7 @@ st_ReadPixels(struct gl_context *ctx, GLint x, GLint y,
> unsigned bind = PIPE_BIND_TRANSFER_READ;
> struct pipe_transfer *tex_xfer;
> ubyte *map = NULL;
> + bool window;
>
> /* Validate state (to be sure we have up-to-date framebuffer surfaces)
> * and flush the bitmap cache prior to reading. */
> @@ -395,24 +474,36 @@ st_ReadPixels(struct gl_context *ctx, GLint x, GLint y,
> return;
> }
>
> - /* See if the texture format already matches the format and type,
> - * in which case the memcpy-based fast path will likely be used and
> - * we don't have to blit. */
> - if (_mesa_format_matches_format_and_type(rb->Format, format,
> - type, pack->SwapBytes, NULL)) {
> - goto fallback;
> - }
> -
> if (needs_integer_signed_unsigned_conversion(ctx, format, type)) {
> goto fallback;
> }
>
> - dst = blit_to_staging(st, strb,
> - st_fb_orientation(ctx->ReadBuffer) == Y_0_TOP,
> - x, y, width, height, format,
> - src_format, dst_format);
> - if (!dst)
> - goto fallback;
> + /* Cache a staging texture for back-to-back ReadPixels, to avoid CPU-GPU
> + * synchronization overhead.
> + */
> + dst = try_cached_readpixels(st, strb,
> + st_fb_orientation(ctx->ReadBuffer) == Y_0_TOP,
> + width, height, format, src_format, dst_format);
> + if (dst) {
> + window = false;
> + } else {
> + /* See if the texture format already matches the format and type,
> + * in which case the memcpy-based fast path will likely be used and
> + * we don't have to blit. */
> + if (_mesa_format_matches_format_and_type(rb->Format, format,
> + type, pack->SwapBytes, NULL)) {
> + goto fallback;
> + }
> +
> + dst = blit_to_staging(st, strb,
> + st_fb_orientation(ctx->ReadBuffer) == Y_0_TOP,
> + x, y, width, height, format,
> + src_format, dst_format);
> + if (!dst)
> + goto fallback;
> +
> + window = true;
> + }
>
> /* map resources */
> pixels = _mesa_map_pbo_dest(ctx, pack, pixels);
> @@ -425,6 +516,9 @@ st_ReadPixels(struct gl_context *ctx, GLint x, GLint y,
> goto fallback;
> }
>
> + if (!window)
> + map += y * tex_xfer->stride + x * util_format_get_blocksize(dst_format);
> +
> /* memcpy data into a user buffer */
> {
> const uint bytesPerRow = width * util_format_get_blocksize(dst_format);
> --
> 2.7.4
>
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