Re: [PATCH V6 2/3] drm/amdgpu: Optimize VM invalidation engine allocation and synchronize GPU TLB flush

["Lazar, Lijo" <lijo.lazar@amd.com>]

On 2/28/2025 3:57 PM, Jesse.zhang@amd.com wrote:
> From: "Jesse.zhang@amd.com" <Jesse.zhang@amd.com>
> 
> - Modify the VM invalidation engine allocation logic to handle SDMA page rings.
>   SDMA page rings now share the VM invalidation engine with SDMA gfx rings instead of
>   allocating a separate engine. This change ensures efficient resource management and
>   avoids the issue of insufficient VM invalidation engines.
> 
> - Add synchronization for GPU TLB flush operations in gmc_v9_0.c.
>   Use spin_lock and spin_unlock to ensure thread safety and prevent race conditions
>   during TLB flush operations. This improves the stability and reliability of the driver,
>   especially in multi-threaded environments.
> 
>  v2: replace the sdma ring check with a function `amdgpu_sdma_is_page_queue`
>  to check if a ring is an SDMA page queue.(Lijo)
> 
>  v3: Add GC version check, only enabled on GC9.4.3/9.4.4/9.5.0
>  v4: Fix code style and add more detailed description (Christian)
> 
> Suggested-by: Lijo Lazar <lijo.lazar@amd.com>
> Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c  | 12 ++++++++++++
>  drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.c | 25 +++++++++++++++++++++++-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.h |  1 +
>  3 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
> index 4eefa17fa39b..aad3c5ea8557 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.c
> @@ -602,8 +602,20 @@ int amdgpu_gmc_allocate_vm_inv_eng(struct amdgpu_device *adev)
>  			return -EINVAL;
>  		}
>  
> +	if (amdgpu_sdma_is_shared_inv_eng(adev, ring)) {
> +		/* SDMA has a special packet which allows it to use the same
> +		 * invalidation engine for all the rings in one instance.
> +		 * Therefore, we do not allocate a separate VM invalidation engine
> +		 * for SDMA page rings. Instead, they share the VM invalidation
> +		 * engine with the SDMA gfx ring. This change ensures efficient
> +		 * resource management and avoids the issue of insufficient VM
> +		 * invalidation engines.
> +		 */
> +		ring->vm_inv_eng = inv_eng - 1;

As mentioned in a previous comment also, strongly discourage to assume
vm_inv_eng based just on loop order. If two rings of the same instance
need to share the inv_eng, call them out explicitly and assign.
Shouldn't have any implicit assumption that the previous/next ring in
the loop order will be part of the same engine.

Thanks,
Lijo

> +	} else {
>  		ring->vm_inv_eng = inv_eng - 1;
>  		vm_inv_engs[vmhub] &= ~(1 << ring->vm_inv_eng);
> +	}
>  
>  		dev_info(adev->dev, "ring %s uses VM inv eng %u on hub %u\n",
>  			 ring->name, ring->vm_inv_eng, ring->vm_hub);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.c
> index 42a7b86e41c3..9b958d6202bc 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.c
> @@ -462,6 +462,29 @@ void amdgpu_sdma_sysfs_reset_mask_fini(struct amdgpu_device *adev)
>  	}
>  }
>  
> +/**
> +* amdgpu_sdma_is_shared_inv_eng - Check if a ring is an SDMA ring that shares a VM invalidation engine
> +* @adev: Pointer to the AMDGPU device structure
> +* @ring: Pointer to the ring structure to check
> +*
> +* This function checks if the given ring is an SDMA ring that shares a VM invalidation engine.
> +* It returns true if the ring is such an SDMA ring, false otherwise.
> +*/
> +bool amdgpu_sdma_is_shared_inv_eng(struct amdgpu_device *adev, struct amdgpu_ring *ring)
> +{
> +	int i = ring->me;
> +
> +	if (!adev->sdma.has_page_queue || i >= adev->sdma.num_instances)
> +		return false;
> +
> +	if (amdgpu_ip_version(adev, GC_HWIP, 0) == IP_VERSION(9, 4, 3) ||
> +	    amdgpu_ip_version(adev, GC_HWIP, 0) == IP_VERSION(9, 4, 4) ||
> +	    amdgpu_ip_version(adev, GC_HWIP, 0) == IP_VERSION(9, 5, 0))
> +		return (ring == &adev->sdma.instance[i].ring);
> +	else
> +		return false;
> +}
> +
>  /**
>   * amdgpu_sdma_register_on_reset_callbacks - Register SDMA reset callbacks
>   * @funcs: Pointer to the callback structure containing pre_reset and post_reset functions
> @@ -503,7 +526,7 @@ int amdgpu_sdma_reset_engine(struct amdgpu_device *adev, uint32_t instance_id, b
>  {
>  	struct sdma_on_reset_funcs *funcs;
>  	int ret = 0;
> -	struct amdgpu_sdma_instance *sdma_instance = &adev->sdma.instance[instance_id];;
> +	struct amdgpu_sdma_instance *sdma_instance = &adev->sdma.instance[instance_id];
>  	struct amdgpu_ring *gfx_ring = &sdma_instance->ring;
>  	struct amdgpu_ring *page_ring = &sdma_instance->page;
>  	bool gfx_sched_stopped = false, page_sched_stopped = false;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.h
> index 965169320065..1fa2049da6c3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sdma.h
> @@ -194,4 +194,5 @@ int amdgpu_sdma_ras_sw_init(struct amdgpu_device *adev);
>  void amdgpu_debugfs_sdma_sched_mask_init(struct amdgpu_device *adev);
>  int amdgpu_sdma_sysfs_reset_mask_init(struct amdgpu_device *adev);
>  void amdgpu_sdma_sysfs_reset_mask_fini(struct amdgpu_device *adev);
> +bool amdgpu_sdma_is_shared_inv_eng(struct amdgpu_device *adev, struct amdgpu_ring *ring);
>  #endif