[Mesa-dev] [PATCH 2/2] RFC: radeon/compute: Limit allocations for VRAM-based chips to 3/4 VRAM

[Aaron Watry]

The CL CTS queries the max allocation size, and then attempts to
allocate buffers of that size. If any of the VRAM is in use, this
causes errors in the radeon kernel module.

It's a bit of a hack, but experimentally on my system, I can use 3/4
of the card's VRAM for a single global/constant buffer allocation given
current GUI/compositor use.

If there's a way to get the actual amount of free VRAM, I'd love to hear about it.

Also, I'm unsure if the radeon kernel module requires all allocated memory to be
contiguous, if so, then we'd need to be able to get at that value.. I'm suspecting
that's not actually the case.

For a 1GB Pitcairn (HD7850) this gets me from the reported clinfo values of:
Global memory size                              2143076352 (1.996GiB)
Max memory allocation                           1500153446 (1.397GiB)
Max constant buffer size                        1500153446 (1.397GiB)

To:
Global memory size                              2143076352 (1.996GiB)
Max memory allocation                           805306368 (768MiB)
Max constant buffer size                        805306368 (768MiB)

Fixes: OpenCL CTS test/conformance/api/min_max_mem_alloc_size,
       OpenCL CTS test/conformance/api/min_max_constant_buffer_size

Signed-off-by: Aaron Watry <awatry at gmail.com>
---
 src/gallium/drivers/radeon/r600_pipe_common.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/gallium/drivers/radeon/r600_pipe_common.c b/src/gallium/drivers/radeon/r600_pipe_common.c
index 2c0cadb030..cdd4062fd3 100644
--- a/src/gallium/drivers/radeon/r600_pipe_common.c
+++ b/src/gallium/drivers/radeon/r600_pipe_common.c
@@ -1144,8 +1144,21 @@ static int r600_get_compute_param(struct pipe_screen *screen,
 		if (ret) {
 			uint64_t *max_mem_alloc_size = ret;
 
-			*max_mem_alloc_size = rscreen->info.max_alloc_size;
-		}
+			uint64_t max_alloc = rscreen->info.max_alloc_size;
+
+			if (rscreen->info.has_dedicated_vram) {
+				/* XXX: Hack to prevent system hangs...
+				 * Limit to 3/4 VRAM for any single allocation.
+				 * Prevents:
+				 *     radeon: Not enough memory for command submission.
+				 */
+				*max_mem_alloc_size = MIN2(
+					rscreen->info.vram_size * 3 / 4, max_alloc
+				);
+			} else {
+				*max_mem_alloc_size = max_alloc;
+			}
+        }
 		return sizeof(uint64_t);
 
 	case PIPE_COMPUTE_CAP_MAX_CLOCK_FREQUENCY:
-- 
2.11.0