Re: [PATCH v2 2/8] v4l: vsp1: Provide a fragment pool

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Kieran,

Thank you for the patch.

On Monday 14 Aug 2017 16:13:25 Kieran Bingham wrote:
> Each display list allocates a body to store register values in a dma
> accessible buffer from a dma_alloc_wc() allocation. Each of these
> results in an entry in the TLB, and a large number of display list
> allocations adds pressure to this resource.
> 
> Reduce TLB pressure on the IPMMUs by allocating multiple display list
> bodies in a single allocation, and providing these to the display list
> through a 'fragment pool'. A pool can be allocated by the display list
> manager or entities which require their own body allocations.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> 
> ---
> v2:
>  - assign dlb->dma correctly
> ---
>  drivers/media/platform/vsp1/vsp1_dl.c | 129 +++++++++++++++++++++++++++-
>  drivers/media/platform/vsp1/vsp1_dl.h |   8 ++-
>  2 files changed, 137 insertions(+)
> 
> diff --git a/drivers/media/platform/vsp1/vsp1_dl.c
> b/drivers/media/platform/vsp1/vsp1_dl.c index cb4625ae13c2..aab9dd6ec0eb
> 100644
> --- a/drivers/media/platform/vsp1/vsp1_dl.c
> +++ b/drivers/media/platform/vsp1/vsp1_dl.c
> @@ -45,6 +45,8 @@ struct vsp1_dl_entry {
>  /**
>   * struct vsp1_dl_body - Display list body
>   * @list: entry in the display list list of bodies
> + * @free: entry in the pool free body list
> + * @pool: pool to which this body belongs
>   * @vsp1: the VSP1 device
>   * @entries: array of entries
>   * @dma: DMA address of the entries
> @@ -54,6 +56,9 @@ struct vsp1_dl_entry {
>   */
>  struct vsp1_dl_body {
>  	struct list_head list;
> +	struct list_head free;
> +
> +	struct vsp1_dl_fragment_pool *pool;
>  	struct vsp1_device *vsp1;
> 
>  	struct vsp1_dl_entry *entries;
> @@ -65,6 +70,30 @@ struct vsp1_dl_body {
>  };
> 
>  /**
> + * struct vsp1_dl_fragment_pool - display list body/fragment pool
> + * @dma: DMA address of the entries
> + * @size: size of the full DMA memory pool in bytes
> + * @mem: CPU memory pointer for the pool
> + * @bodies: Array of DLB structures for the pool
> + * @free: List of free DLB entries
> + * @lock: Protects the pool and free list
> + * @vsp1: the VSP1 device
> + */
> +struct vsp1_dl_fragment_pool {
> +	/* DMA allocation */
> +	dma_addr_t dma;
> +	size_t size;
> +	void *mem;
> +
> +	/* Body management */
> +	struct vsp1_dl_body *bodies;
> +	struct list_head free;
> +	spinlock_t lock;
> +
> +	struct vsp1_device *vsp1;
> +};
> +
> +/**
>   * struct vsp1_dl_list - Display list
>   * @list: entry in the display list manager lists
>   * @dlm: the display list manager
> @@ -104,6 +133,7 @@ enum vsp1_dl_mode {
>   * @active: list currently being processed (loaded) by hardware
>   * @queued: list queued to the hardware (written to the DL registers)
>   * @pending: list waiting to be queued to the hardware
> + * @pool: fragment pool for the display list bodies
>   * @gc_work: fragments garbage collector work struct
>   * @gc_fragments: array of display list fragments waiting to be freed
>   */
> @@ -119,6 +149,8 @@ struct vsp1_dl_manager {
>  	struct vsp1_dl_list *queued;
>  	struct vsp1_dl_list *pending;
> 
> +	struct vsp1_dl_fragment_pool *pool;
> +
>  	struct work_struct gc_work;
>  	struct list_head gc_fragments;
>  };
> @@ -128,6 +160,103 @@ struct vsp1_dl_manager {
>   */
> 
>  /*
> + * Fragment pool's reduce the pressure on the iommu TLB by allocating a
> single
> + * large area of DMA memory and allocating it as a pool of fragment bodies
> + */

Could you document non-static function using kerneldoc ? Parameters to this 
function would benefit from some documentation. I'd also like to see the 
fragment get/put functions documented, as you remove existing kerneldoc for 
the alloc/free existing functions in patch 3/8.

> +struct vsp1_dl_fragment_pool *
> +vsp1_dl_fragment_pool_alloc(struct vsp1_device *vsp1, unsigned int qty,

I think I would name this function vsp1_dl_fragment_pool_create(), as it does 
more than just allocating memory. Similarly I'd call the free function 
vsp1_dl_fragment_pool_destroy().

qty is a bit vague, I'd rename it to num_fragments.

> +			    unsigned int num_entries, size_t extra_size)
> +{
> +	struct vsp1_dl_fragment_pool *pool;
> +	size_t dlb_size;
> +	unsigned int i;
> +
> +	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
> +	if (!pool)
> +		return NULL;
> +
> +	pool->vsp1 = vsp1;
> +
> +	dlb_size = num_entries * sizeof(struct vsp1_dl_entry) + extra_size;

extra_size is only used by vsp1_dlm_create(), to allocate extra memory for the 
display list header. We need one header per display list, not per display list 
body.

> +	pool->size = dlb_size * qty;
> +
> +	pool->bodies = kcalloc(qty, sizeof(*pool->bodies), GFP_KERNEL);
> +	if (!pool->bodies) {
> +		kfree(pool);
> +		return NULL;
> +	}
> +
> +	pool->mem = dma_alloc_wc(vsp1->bus_master, pool->size, &pool->dma,
> +					    GFP_KERNEL);

This is a weird indentation.

> +	if (!pool->mem) {
> +		kfree(pool->bodies);
> +		kfree(pool);
> +		return NULL;
> +	}
> +
> +	spin_lock_init(&pool->lock);
> +	INIT_LIST_HEAD(&pool->free);
> +
> +	for (i = 0; i < qty; ++i) {
> +		struct vsp1_dl_body *dlb = &pool->bodies[i];
> +
> +		dlb->pool = pool;
> +		dlb->max_entries = num_entries;
> +
> +		dlb->dma = pool->dma + i * dlb_size;
> +		dlb->entries = pool->mem + i * dlb_size;
> +
> +		list_add_tail(&dlb->free, &pool->free);
> +	}
> +
> +	return pool;
> +}
> +
> +void vsp1_dl_fragment_pool_free(struct vsp1_dl_fragment_pool *pool)
> +{
> +	if (!pool)
> +		return;

Can this happen ?

> +
> +	if (pool->mem)
> +		dma_free_wc(pool->vsp1->bus_master, pool->size, pool->mem,
> +			    pool->dma);
> +
> +	kfree(pool->bodies);
> +	kfree(pool);
> +}
> +
> +struct vsp1_dl_body *vsp1_dl_fragment_get(struct vsp1_dl_fragment_pool
> *pool)
> +{
> +	struct vsp1_dl_body *dlb = NULL;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&pool->lock, flags);
> +
> +	if (!list_empty(&pool->free)) {
> +		dlb = list_first_entry(&pool->free, struct vsp1_dl_body, 
free);
> +		list_del(&dlb->free);
> +	}
> +
> +	spin_unlock_irqrestore(&pool->lock, flags);
> +
> +	return dlb;
> +}
> +
> +void vsp1_dl_fragment_put(struct vsp1_dl_body *dlb)
> +{
> +	unsigned long flags;
> +
> +	if (!dlb)
> +		return;
> +
> +	dlb->num_entries = 0;
> +
> +	spin_lock_irqsave(&dlb->pool->lock, flags);
> +	list_add_tail(&dlb->free, &dlb->pool->free);
> +	spin_unlock_irqrestore(&dlb->pool->lock, flags);
> +}
> +
> +/*
>   * Initialize a display list body object and allocate DMA memory for the
> body * data. The display list body object is expected to have been
> initialized to * 0 when allocated.
> diff --git a/drivers/media/platform/vsp1/vsp1_dl.h
> b/drivers/media/platform/vsp1/vsp1_dl.h index ee3508172f0a..9528484a8a34
> 100644
> --- a/drivers/media/platform/vsp1/vsp1_dl.h
> +++ b/drivers/media/platform/vsp1/vsp1_dl.h
> @@ -17,6 +17,7 @@
> 
>  struct vsp1_device;
>  struct vsp1_dl_fragment;
> +struct vsp1_dl_fragment_pool;

I noticed that the vsp1_dl_fragment structure is declared here but never 
defined or used. The vsp1_dl_fragment_* functions all operate on vsp1_dl_body 
structures.

The name body is used in the datasheet, so I think it would make sense to 
s/fragments/bodies/ and s/fragment/body/ through the code as a prerequisite 
for this patch, and rebasing it accordingly.

>  struct vsp1_dl_list;
>  struct vsp1_dl_manager;
> 
> @@ -34,6 +35,13 @@ void vsp1_dl_list_put(struct vsp1_dl_list *dl);
>  void vsp1_dl_list_write(struct vsp1_dl_list *dl, u32 reg, u32 data);
>  void vsp1_dl_list_commit(struct vsp1_dl_list *dl);
> 
> +struct vsp1_dl_fragment_pool *
> +vsp1_dl_fragment_pool_alloc(struct vsp1_device *vsp1, unsigned int qty,
> +			    unsigned int num_entries, size_t extra_size);
> +void vsp1_dl_fragment_pool_free(struct vsp1_dl_fragment_pool *pool);
> +struct vsp1_dl_body *vsp1_dl_fragment_get(struct vsp1_dl_fragment_pool
> *pool);
> +void vsp1_dl_fragment_put(struct vsp1_dl_body *dlb);
> +
>  struct vsp1_dl_body *vsp1_dl_fragment_alloc(struct vsp1_device *vsp1,
>  					    unsigned int num_entries);
>  void vsp1_dl_fragment_free(struct vsp1_dl_body *dlb);
a
-- 
Regards,

Laurent Pinchart