On 2024-05-06 16:30, Felix Kuehling wrote:
>
> On 2024-05-03 18:06, Harish Kasiviswanathan wrote:
>> gpu_id needs to be unique for user space to identify GPUs via KFD
>> interface. In the current implementation there is a very small
>> probability of having non unique gpu_ids.
>>
>> v2: Add check to confirm if gpu_id is unique. If not unique, find one
>> Changed commit header to reflect the above
>>
>> Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@xxxxxxx>
>> ---
>> drivers/gpu/drm/amd/amdkfd/kfd_topology.c | 26 ++++++++++++++++++++++-
>> 1 file changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
>> index b93913934b03..01d4c2e10c6d 100644
>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_topology.c
>> @@ -1095,6 +1095,8 @@ static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>> uint32_t hashout;
>> uint32_t buf[8];
>> uint64_t local_mem_size;
>> + struct kfd_topology_device *dev;
>> + bool is_unique;
>> int i;
>> if (!gpu)
>> @@ -1115,6 +1117,28 @@ static uint32_t kfd_generate_gpu_id(struct kfd_node *gpu)
>> for (i = 0, hashout = 0; i < 8; i++)
>> hashout ^= hash_32(buf[i], KFD_GPU_ID_HASH_WIDTH);
>> + /* hash generated could be non-unique. Check if it is unique.
>> + * If not unique increment till unique one is found. In case
>> + * of overflow, restart from 1
>> + */
>> + down_read(&topology_lock);
>> + do {
>> + is_unique = true;
>> + list_for_each_entry(dev, &topology_device_list, list) {
>> + if (dev->gpu && dev->gpu_id == hashout) {
>> + is_unique = false;
>> + break;
>> + }
>> + }
>> + if (unlikely(!is_unique)) {
>> + hashout = (hashout + 1) &
>> + ((1 << KFD_GPU_ID_HASH_WIDTH) - 1);
>> + if (!hashout)
>> + hashout = 1;
>
> This doesn't catch the case that hashout was 0 before incrementing it, and was found to be unique.
I didn't actively think about this case when I sent the patch out. However, we don't have gpu_id to be 0. There are places where gpu_id=0 means it is CPU node
>
> Regards,
> Felix
>
>
>> + }
>> + } while (!is_unique);
>> + up_read(&topology_lock);
>> +
>> return hashout;
>> }
>> /* kfd_assign_gpu - Attach @gpu to the correct kfd topology device. If
>> @@ -1946,7 +1970,6 @@ int kfd_topology_add_device(struct kfd_node *gpu)
>> struct amdgpu_gfx_config *gfx_info = &gpu->adev->gfx.config;
>> struct amdgpu_cu_info *cu_info = &gpu->adev->gfx.cu_info;
>> - gpu_id = kfd_generate_gpu_id(gpu);
>> if (gpu->xcp && !gpu->xcp->ddev) {
>> dev_warn(gpu->adev->dev,
>> "Won't add GPU to topology since it has no drm node assigned.");
>> @@ -1969,6 +1992,7 @@ int kfd_topology_add_device(struct kfd_node *gpu)
>> if (res)
>> return res;
>> + gpu_id = kfd_generate_gpu_id(gpu);
>> dev->gpu_id = gpu_id;
>> gpu->id = gpu_id;
>>
