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cogl: remove mesa_46631_slow_read_pixels_workaround

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This function gets hit even today on relatively modern Intel systems (I
have a Haswell Desktop with Mesa 18.2.4) if the pixel format is right.
Presumably it makes things slower for no longer a reason.

According to cb146dc515, this
functionality was refactored into a workaround path in 2012. The commit
message mentions the problem existing before Mesa 8.0.2. The number
refers to https://bugs.freedesktop.org/show_bug.cgi?id=46631 .

The use case where I hit this is when improving support for DisplayLink
video outputs. These are used through a "secondary GPU", and since
DisplayLink does not have a GPU, Mutter uses the CPU copy path with Cogl
read-pixels[1]. If the DisplayLink framebuffer was allocated as
DRM_FORMAT_XRGB8888 (the only format it currently handles correctly),
mesa_46631_slow_read_pixels_workaround would get hit. The render buffer is
the same format as the framebuffer, yet doing the copy XRGB -> XRGB ends
up being slower than XRGB -> XBGR which makes no sense.

This patch is not sufficient to fix the XRGB -> XRGB copy performance,
but it is required.

This patch reverts CoglGpuInfoDriverBug into what it was before
cb146dc515.

[1] This is not actually true until
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/278 is
    merged.
This commit is contained in:
Pekka Paalanen 2018-11-06 14:31:53 +02:00 committed by Ray Strode
parent f6f188dad4
commit c8112a1dbc
3 changed files with 2 additions and 139 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
cogl/cogl/cogl-gpu-info-private.h
View File

@ -74,12 +74,7 @@ typedef enum
typedef enum
{
/* If this bug is present then it is faster to read pixels into a
* PBO and then memcpy out of the PBO into system memory rather than
* directly read into system memory.
* https://bugs.freedesktop.org/show_bug.cgi?id=46631
*/
COGL_GPU_INFO_DRIVER_BUG_MESA_46631_SLOW_READ_PIXELS = 1 << 0
COGL_GPU_INFO_DRIVER_STUB
} CoglGpuInfoDriverBug;
typedef struct _CoglGpuInfoVersion CoglGpuInfoVersion;

10
cogl/cogl/cogl-gpu-info.c
View File

@ -568,13 +568,5 @@ probed:
gpu->architecture_name);
/* Determine the driver bugs */
/* In Mesa the glReadPixels implementation is really slow
when using the Intel driver. The Intel
driver has a fast blit path when reading into a PBO. Reading into
a temporary PBO and then memcpying back out to the application's
memory is faster than a regular glReadPixels in this case */
if (gpu->vendor == COGL_GPU_INFO_VENDOR_INTEL &&
gpu->driver_package == COGL_GPU_INFO_DRIVER_PACKAGE_MESA)
gpu->driver_bugs |= COGL_GPU_INFO_DRIVER_BUG_MESA_46631_SLOW_READ_PIXELS;
gpu->driver_bugs = 0;
}

124
cogl/cogl/driver/gl/cogl-framebuffer-gl.c
View File

@ -1240,96 +1240,6 @@ _cogl_framebuffer_gl_draw_indexed_attributes (CoglFramebuffer *framebuffer,
_cogl_buffer_gl_unbind (buffer);
}
static CoglBool
mesa_46631_slow_read_pixels_workaround (CoglFramebuffer *framebuffer,
int x,
int y,
CoglReadPixelsFlags source,
CoglBitmap *bitmap,
CoglError **error)
{
CoglContext *ctx;
CoglPixelFormat format;
CoglBitmap *pbo;
int width;
int height;
CoglBool res;
uint8_t *dst;
const uint8_t *src;
ctx = cogl_framebuffer_get_context (framebuffer);
width = cogl_bitmap_get_width (bitmap);
height = cogl_bitmap_get_height (bitmap);
format = cogl_bitmap_get_format (bitmap);
pbo = cogl_bitmap_new_with_size (ctx, width, height, format);
/* Read into the pbo. We need to disable the flipping because the
blit fast path in the driver does not work with
GL_PACK_INVERT_MESA is set */
res = _cogl_framebuffer_read_pixels_into_bitmap (framebuffer,
x, y,
source |
COGL_READ_PIXELS_NO_FLIP,
pbo,
error);
if (!res)
{
cogl_object_unref (pbo);
return FALSE;
}
/* Copy the pixels back into application's buffer */
dst = _cogl_bitmap_map (bitmap,
COGL_BUFFER_ACCESS_WRITE,
COGL_BUFFER_MAP_HINT_DISCARD,
error);
if (!dst)
{
cogl_object_unref (pbo);
return FALSE;
}
src = _cogl_bitmap_map (pbo,
COGL_BUFFER_ACCESS_READ,
0, /* hints */
error);
if (src)
{
int src_rowstride = cogl_bitmap_get_rowstride (pbo);
int dst_rowstride = cogl_bitmap_get_rowstride (bitmap);
int to_copy =
_cogl_pixel_format_get_bytes_per_pixel (format) * width;
int y;
/* If the framebuffer is onscreen we need to flip the
data while copying */
if (!cogl_is_offscreen (framebuffer))
{
src += src_rowstride * (height - 1);
src_rowstride = -src_rowstride;
}
for (y = 0; y < height; y++)
{
memcpy (dst, src, to_copy);
dst += dst_rowstride;
src += src_rowstride;
}
_cogl_bitmap_unmap (pbo);
}
else
res = FALSE;
_cogl_bitmap_unmap (bitmap);
cogl_object_unref (pbo);
return res;
}
CoglBool
_cogl_framebuffer_gl_read_pixels_into_bitmap (CoglFramebuffer *framebuffer,
int x,
@ -1350,40 +1260,6 @@ _cogl_framebuffer_gl_read_pixels_into_bitmap (CoglFramebuffer *framebuffer,
CoglBool pack_invert_set;
int status = FALSE;
/* Workaround for cases where its faster to read into a temporary
* PBO. This is only worth doing if:
*
* • The GPU is an Intel GPU. In that case there is a known
* fast-path when reading into a PBO that will use the blitter
* instead of the Mesa fallback code. The driver bug will only be
* set if this is the case.
* • We're not already reading into a PBO.
* • The target format is BGRA. The fast-path blit does not get hit
* otherwise.
* • The size of the data is not trivially small. This isn't a
* requirement to hit the fast-path blit but intuitively it feels
* like if the amount of data is too small then the cost of
* allocating a PBO will outweigh the cost of temporarily
* converting the data to floats.
*/
if ((ctx->gpu.driver_bugs &
COGL_GPU_INFO_DRIVER_BUG_MESA_46631_SLOW_READ_PIXELS) &&
(width > 8 || height > 8) &&
(format & ~COGL_PREMULT_BIT) == COGL_PIXEL_FORMAT_BGRA_8888 &&
cogl_bitmap_get_buffer (bitmap) == NULL)
{
CoglError *ignore_error = NULL;
if (mesa_46631_slow_read_pixels_workaround (framebuffer,
x, y,
source,
bitmap,
&ignore_error))
return TRUE;
else
cogl_error_free (ignore_error);
}
_cogl_framebuffer_flush_state (framebuffer,
framebuffer,
COGL_FRAMEBUFFER_STATE_BIND);