[Mesa-dev] [PATCH 0/2] radeon: Use the DMA engine for buffer downloads

[Niels Ole Salscheider]

On Tuesday 04 March 2014, 02:08:58, Marek Olšák wrote:
> Could you please do this without changing u_upload_mgr? You can still
> use u_upload_alloc to allocate buffer memory in the driver and the map
> buffer read/write flags are not important with persistent coherent
> buffer mappings anyway.

Since 150ac07b855b5c5f879bf6ce9ca421ccd1a6c938 we allocate CPU -> GPU 
streaming buffers (i. e. those with PIPE_USAGE_STREAM) in VRAM.
We should therefore set buffer.usage to PIPE_USAGE_STAGING in 
u_upload_alloc_buffer when we use u_upload_mgr for downloads - otherwise we 
won't get any performance improvements.
Would it now be OK to change u_upload_mgr or do you have a better proposal?

Ole

> Marek
> 
> On Mon, Mar 3, 2014 at 9:29 PM, Niels Ole Salscheider
> 
> <niels_ole at salscheider-online.de> wrote:
> > Using the DMA engine for buffer downloads vastly improves performance.
> > This is because reads from VRAM by the CPU are slow because of the high
> > latency of the PCIe bus.
> > 
> > The first patch allows u_upload_mgr to be used for downloads, too. The
> > second patch then uses u_upload_mgr in the radeon driver for downloads.
> > I considered to rename u_upload_mgr to u_transfer_mgr since it might be
> > confusing that an "upload manager" can be used for downloads. But then
> > again we also have "transfers" so that u_transfer_mgr might also be
> > confusing. Thus, I decided not to rename it for now.
> > 
> > Without these patches, the buffer_bandwidth benchmark from uCLbench gives
> > me:
> > 
> > ./buffer_bandwidth --size=20000000 --iterations=100
> > # device 0: AMD BARTS // type gpu (192 MB global memory, 64 KB constant
> > memory,> 
> >     32 KB local memory)
> > 
> > 1/1 direct     20000000 Bytes   759.29 MB/s(HD)         17.13 MB/s(DD)
> > 
> >         14.61 MB/s(DH)
> > 
> > With these paches, the read performance is much better:
> > 
> > ./buffer_bandwidth --size=20000000 --iterations=100
> > # device 0: AMD BARTS // type gpu (192 MB global memory, 64 KB constant
> > memory,> 
> >     32 KB local memory)
> > 
> > 1/1 direct     20000000 Bytes   759.90 MB/s(HD)         613.49 MB/s(DD)
> > 
> >         1841.07 MB/s(DH)
> > 
> > Judging by these numbers, it might even make sense to use the DMA engine
> > for larger buffer downloads...
> > 
> > Niels Ole Salscheider (2):
> >   util/u_upload_mgr: Allow to also use it for downloads
> >   radeon: Use transfer manager for buffer downloads
> >  
> >  src/gallium/auxiliary/hud/hud_context.c         |  3 +-
> >  src/gallium/auxiliary/util/u_blitter.c          |  3 +-
> >  src/gallium/auxiliary/util/u_upload_mgr.c       | 49 +++++++++++-----
> >  src/gallium/auxiliary/util/u_upload_mgr.h       | 13 ++++-
> >  src/gallium/auxiliary/util/u_vbuf.c             |  3 +-
> >  src/gallium/auxiliary/vl/vl_compositor.c        |  3 +-
> >  src/gallium/drivers/ilo/ilo_context.c           |  3 +-
> >  src/gallium/drivers/r300/r300_context.c         |  3 +-
> >  src/gallium/drivers/radeon/r600_buffer_common.c | 78
> >  +++++++++++++++++++------ src/gallium/drivers/radeon/r600_pipe_common.c 
> >   | 14 ++++-
> >  src/gallium/drivers/radeon/r600_pipe_common.h   |  1 +
> >  src/mesa/state_tracker/st_context.c             |  9 ++-
> >  12 files changed, 136 insertions(+), 46 deletions(-)
> > 
> > --
> > 1.9.0
> > 
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