Background:
amdkfd needs GART memory for several things, such as runlist packets, MQDs, HPDs and more. Unfortunately, all of this memory must be always pinned (due to several reasons which were discussed during the initial review of amdkfd).
Current Solution:
The current (short/mid-term) solution that was proposed by Jerome.G, is to limit the amount of memory to a small size, roughly 4MB and allocate this buffer at the start of the GART. To accomodate this, amdkfd has two kernel module parameters, maximum number of HSA processes and maximum number of queues per process, which require under 4MB of GART memory when using their defaults, 32 and 128 respectively.
Until now, amdkfd used the radeon sub-allocator module (radeon_sa) to handle the sub-allocation of memory from this large buffer to different modules inside the amdkfd.
However, while running OpenCL conformance test suite, we found that radeon_sa module is not suitable for this kind of task, due to its design: 1. Every allocation increments its interal pointer so the next allocation is *always* done ahead of the previous allocation. This causes the internal pointer to wrap-around when it reaches the end of the buffer.
2. When encoutering an area that is already allocated, the module waits for that area to be freed. If it is not freed in a timely manner (or has no fence), the allocation fails. Simply put, it can't "skip" the allocated area.
Now, this is most probably good for graphics, but for amdkfd needs, the combination of the two behaviors mentioned above eventually causes a denial-of-service. This is because some memory allocations are *always* present and *never* freed (such as HPDs). Therefore, given enough time and workload, the radeon_sa eventually wraps around, encounters an already allocated area and gets stuck.
Proposed new solution:
To solve this, I have written a simple sub-allocator module inside amdkfd. It allocates fixed-size contiguous chunks (1 or more) and uses a bitmap to manage the allocations. The next allocation is always being searched for from the start of the GART buffer, and the module knows how to skip allocated chunks.
Because most allocations are MQDs, and MQDs are 512 Bytes in size, I set the default chunk size to be 512 Bytes.
The basic GART memory allocation is still being done in the amdkfd <--> radeon interface, and it still occupies less than 4MB.
I have chosen to implement a new allocator instead of changing radeon_sa because the behavior of radeon_sa is very appropriate for graphics, where allocations do not stay forever. Also, amdkfd doesn't actually need the flexibility and features radeon_sa provides.
Oded
Oded Gabbay (9): drm/amd: Add new kfd-->kgd interface for gart usage drm/radeon: Impl. new gtt allocate/free functions drm/amdkfd: Add gtt sa related data to kfd_dev struct drm/amdkfd: Add kfd gtt sub-allocator functions drm/amdkfd: Fixed calculation of gart buffer size drm/amdkfd: Allocate gart memory using new interface drm/amdkfd: Using new gtt sa in amdkfd drm/radeon: Remove old radeon_sa usage from kfd-->kgd interface drm/amd: Remove old radeon_sa funcs from kfd-->kgd interface
drivers/gpu/drm/amd/amdkfd/kfd_device.c | 217 ++++++++++++++++++++- .../gpu/drm/amd/amdkfd/kfd_device_queue_manager.c | 23 +-- drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c | 41 ++-- drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager.c | 16 +- drivers/gpu/drm/amd/amdkfd/kfd_packet_manager.c | 10 +- drivers/gpu/drm/amd/amdkfd/kfd_priv.h | 28 ++- drivers/gpu/drm/amd/include/kgd_kfd_interface.h | 23 +-- drivers/gpu/drm/radeon/radeon_kfd.c | 128 ++++++------ 8 files changed, 329 insertions(+), 157 deletions(-)