Mesa (main): anv: Lower bufferImageGranularity to 1 from 64

[GitLab Mirror]

Module: Mesa
Branch: main
Commit: 4ed9fd62c9135cae21907cac7227725668dfd745
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=4ed9fd62c9135cae21907cac7227725668dfd745

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Thu Feb 17 02:08:33 2022 -0800

anv: Lower bufferImageGranularity to 1 from 64

The Vulkan 1.3 spec says:

   "The implementation-dependent limit bufferImageGranularity specifies
    a page-like granularity at which linear and non-linear resources
    must be placed in adjacent memory locations to avoid aliasing.  Two
    resources which do not satisfy this granularity requirement are said
    to alias. bufferImageGranularity is specified in bytes, and must be
    a power of two.  Implementations which do not impose a granularity
    restriction may report a bufferImageGranularity value of one.

    Note: Despite its name, bufferImageGranularity is really a
    granularity between "linear" and "non-linear" resources."

We set this limit to 64 bytes (a cacheline) at the dawn of time, without
any real rationale attached.  There shouldn't be any restrictions here.
Our tile sizes are typically 4K, and tiled resource addresses are
aligned to the tile size, and the extent is also a multiple of the tile
sized.  So if a linear resource occurs before a tiled one, there will
naturally be some space due to the alignment of the tiled resource's
starting address.  If a linear resource occurs after a tiled one, the
tiled resource's ending address is already 4K aligned, which is already
guaranteeing that they won't share a cacheline.

So I think it should be fine to reduce this to 1.  The other Vulkan
driver for our hardware seems to advertise 1 here as well.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15066>

---

 src/intel/vulkan/anv_device.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/intel/vulkan/anv_device.c b/src/intel/vulkan/anv_device.c
index 3bdb9d40cf2..3ce0a4e6f21 100644
--- a/src/intel/vulkan/anv_device.c
+++ b/src/intel/vulkan/anv_device.c
@@ -1840,7 +1840,7 @@ void anv_GetPhysicalDeviceProperties(
       .maxPushConstantsSize                     = MAX_PUSH_CONSTANTS_SIZE,
       .maxMemoryAllocationCount                 = UINT32_MAX,
       .maxSamplerAllocationCount                = 64 * 1024,
-      .bufferImageGranularity                   = 64, /* A cache line */
+      .bufferImageGranularity                   = 1,
       .sparseAddressSpaceSize                   = 0,
       .maxBoundDescriptorSets                   = MAX_SETS,
       .maxPerStageDescriptorSamplers            = max_samplers,