[Answer myself for some of the questions] On Mon, Mar 28, 2011 at 3:35 PM, Chia-I Wu <olva...@gmail.com> wrote: > Hi list, > > I have a simple scenario that there are clients rendering to buffer > objects using the CPU, and the display server compositing the buffers > using OpenGL and doing page flips to present the final contents. It > is like doing the following steps repeatedly > > 1) process A (the server) allocates a bo > > bo = radeon_bo_open(info->bufmgr, 0, size, align, RADEON_GEM_DOMAIN_GTT, 0); > > 2) process B (the client) maps the bo for CPU rendering and unmaps > > radeon_bo_map(bo, 1); > /* ...render with CPU... */ > radeon_bo_unmap(bo); > > 3) process A renders to the back buffer using the bo as the texture > > /* renders with OpenGL followed by a glFinish() */ > > 4) process A flips its front and back buffers > > drmModePageFlip(fd, crtc_id, fb_id_of_the_bo, 0x0, NULL); > drmWaitVBlank(fd, &vbl); /* HACK! wait until the next vblank */ > > With this setup, I am seeing glitches frequently. My hardware is a > CEDAR. The kernel is 2.6.38-rc7 and both mesa and drm are from > master. I originally ran them on a i965-based machine using > libdrm_i915, and it is fine there. > > I think there are sync issues in how I use libdrm_radeon, but I could > not identify them. Here are my findings/questions > > In 1), The bo is initially in the GTT domain because CPU rendering is > expected. Using VRAM domain reduces the glitches greatly, but there > are still glitches and the framerate is much lower. > > In 3), glFinish() is called after rendering to make sure the frame is > complete before page flipping. Does glFlush() suffice here? I think > that would require page flipping to be pipelined, but I am not sure if > that is the case with radeon. Yes, it should pipelined. glFlush() suffices here. > > In 4), The kernel does not block rendering to the back buffer (which > was the front buffer before flipping) until the flip takes place. I > think the kernel driver should be fixed because, in drm_crtc.h, it > says "the implementation must return immediately and block all > rendering to the current fb until the flip has completed". To > workaround that, I do a drmWaitVBlank() call as a hacky way to wait > for the flip to complete. > > But they still do not explain the glitches I am seeing (with my limited > understanding of radeon). The hack in 4) does not work as expected. The right way to wait for the page flip to take place is to call drmModePageFlip with DRM_MODE_PAGE_FLIP_EVENT and do a blocking read. With this change, the glitches are gone (visually). But this is still a workaround and the kernel driver should be fixed.
> Regards, > olv > -- o...@lunarg.com _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/dri-devel
