On Fri, Aug 13, 2010 at 5:25 PM, Chia-I Wu <olva...@gmail.com> wrote: > On Fri, Aug 13, 2010 at 11:35 PM, Keith Whitwell <kei...@vmware.com> wrote: >> On Fri, 2010-08-13 at 08:09 -0700, Chia-I Wu wrote: >>> On Fri, Aug 13, 2010 at 10:51 PM, Keith Whitwell <kei...@vmware.com> wrote: >>> > On Fri, 2010-08-13 at 07:46 -0700, Chia-I Wu wrote: >>> >> On Fri, Aug 13, 2010 at 10:14 PM, Keith Whitwell <kei...@vmware.com> >>> >> wrote: >>> >> > On Fri, 2010-08-13 at 07:04 -0700, Chia-I Wu wrote: >>> >> >> Hi, >>> >> >> >>> >> >> There are two primitive transformations in gallium draw module. In >>> >> >> varray, primitives are "split"ted. When a primitive has more vertices >>> >> >> than the middle end can handle, varray splits the primitive and calls >>> >> >> the middle end multiple times. >>> >> >> >>> >> >> In vcache, primitives are "decompose"d. More advanced primitives are >>> >> >> decomposed into one of point, line(_adj), or triangle(_adj). >>> >> >> Similarly, vcache may call the middle end multiple times to flush its >>> >> >> internal buffer. In some cases, vcache passes the primitves through >>> >> >> without decomposing nor splitting, as can be seen in vcache_check_run. >>> >> >> >>> >> >> The issue with vcache is that it has to decompose a primitive >>> >> >> differently depending on the provoking convention, as explained in >>> >> >> >>> >> >> >>> >> >> http://lists.freedesktop.org/archives/mesa-dev/2010-August/001797.html >>> >> >> >>> >> >> It becomes a problem when GS is active. >>> >> >> >>> >> >> My proposal is to make vcache split instead of decompose. Because >>> >> >> varray only splits and vcache has a pass-through path, the rest of the >>> >> >> workflow already has to support all primitive types. Switching from >>> >> >> decompose to split does not require a big change to the rest of the >>> >> >> workflow. >>> >> >> >>> >> >> But then vcache will look a lot like varray, only with indexed >>> >> >> primitive support. It leads me to a new frontend that replaces both >>> >> >> varray and vcache: vsplit >>> >> >> >>> >> >> http://cgit.freedesktop.org/~olv/mesa/log/?h=draw-vsplit >>> >> >> >>> >> >> vsplit is based on varray. It uses some code from vcache to support >>> >> >> indexed primitives. When vcache decomposes, there are flags being set >>> >> >> to indicate that if the stipple counter should be reset or if some >>> >> >> edge of a triangle should be omitted in unfilled mode. The segments >>> >> >> of a splitted primitive have flags for similar purposes too: >>> >> >> >>> >> >> DRAW_SPLIT_AFTER More segments to come after this one >>> >> >> DRAW_SPLIT_BEFORE There are preceding segments >>> >> >> >>> >> >> These flags are set by vsplit and the middle ends pass them to the >>> >> >> other stages. Therefore, the run methods of middle ends are augmented >>> >> >> to take the flags. >>> >> >> >>> >> >> To summarize, vsplit >>> >> >> >>> >> >> - fixes GS when (flatshade && flatshade_first) is on >>> >> >> - never sends more vertices than the middle end claims to handle >>> >> >> - is faster than vcache: split instead of decompose, no get_elt >>> >> >> calls >>> >> >> - no longer uses the higher bits of draw_elts for stipple/edge flags >>> >> >> >>> >> >> Suggestions? >>> >> > >>> >> > >>> >> > Hi - I haven't looked at the patches yet, but a couple of questions: >>> >> > >>> >> > How does this interact with the draw_pipe_* code - which requires >>> >> > decomposed primitives? >>> >> draw_pipe.c decomposes the primitives. It is there before because it >>> >> has to support varray and vcache_check_run which do not decompose. >>> > >>> > OK. >>> > >>> >> > How does this cope with indexed rendering where the vertex buffers >>> >> > themselves are too large (for hardware or some other entity)? Eg. >>> >> > imagine the hardware could cope with up to 64k vertices, and you have a >>> >> > drawelements call randomly referencing vertices in range 0..128k ? >>> >> Vertex fetching happens in the middle end so the range of the indices >>> >> is not a problem. Though vsplit guarantees that it never calls the >>> >> middle end with more vertices than the middle end claims to support >>> >> (as returned by draw_pt_middle_end::prepare). The limit is usually >>> >> decidied by the size of the buffer for vertex emitting. >>> > >>> > I guess I'm wondering how it does this. If the middle end says it >>> > supports 64k vertices, and the vertex element looks like >>> > >>> > [0, 128k, 64k, 32k, 96k, 16k, 1, ... ] >>> > >>> > what gets sent? (Sorry, I still haven't looked at the code, you could >>> > well have addressed this). >>> I see. The frontend would set >>> >>> fetch_elts = [0, 128k, 64k, 32k, 96k, 16k, 1, ... ] >>> draw_elts = [0, 1, 2, 3, 4, 5, 6, ...] >>> >>> fetch_elts is processed by the middle end and it will fetch the given >>> vertices. draw_elts will be passed to draw_emit or the pipeline. It >>> is the new index buffer, which indexes into the fetched vertices. >>> >>> It is actual the same as vcache. So when fetch_elts is >>> >>> [0, 128k, 64k, 64k, 128k, 16k, ...], >>> >>> draw_elts would be set to >>> >>> [0, 1, 2, 2, 1, 3, ...] >>> >>> The number of elements to fetch (and shade) is minimized. >> >> Thanks Chia-I, I've taken a look at the code & this makes sense - the >> fetch/draw cache is still there, but specialized into 4 versions for >> each element type. And it seems like you take some steps not to hit it >> unnecessarily. >> >> I'm coming up to speed on it though, so a couple more questions - for >> fan primitives, it seems like you always end up in the segment_cache >> code -- is that true, or is there a fastpath I missed? In particular, >> if the whole fan fits within the limits of the middle end, will it still >> end up going through the cache? > Yes, if it exceeds vsplit's limit (SEGMENT_SIZE). >> Actually it looks like this happens in an early-out at the bottom of the >> patch: >> >> >> + /* no splitting required */ >> + if (count <= max_count_simple) { >> + SEGMENT_SIMPLE(0x0, start, count); >> + } >> >> >> where max_count_simple is either >> >> vsplit->max_vertices >> or >> vsplit->segment_size (for indexed primitives) >> >> These in turn are generated as: >> >> + middle->prepare(middle, vsplit->prim, opt, &vsplit->max_vertices); >> + >> + vsplit->segment_size = MIN2(SEGMENT_SIZE, vsplit->max_vertices); >> >> and SEGMENT_SIZE is 1024. >> >> >> So any indexed primitive where the number of vertices (or is it number >> of indices) exceeds 1024, will end up on the cache path? >> I know this used to be true as well -- just wondering if there is a way >> to improve on this... > max_count_simple is set to the segment size (<= 1024) because the > middle end expects draw_elts to be of type ushort. vsplit needs to > use its internal fixed-size buffer when the index_size!=2. > > The limit may be lifted for index_size==2. The attached patch should > relax the limit (untested as it is getting late here :-). Another way > that comes to my mind now is to make the internal buffer dynamically > sized, and make SEGMENT_SIZE a large limit on the dynamic size. >
I think this all makes a great followon change, but as a first step vsplit looks very nice - a welcome cleanup of the existing code. Keith _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
