Re: [PATCH v3 7/9] xen/blkback: separate ring information out of struct xen_blkif

["Roger Pau Monné" <roger.pau@citrix.com>]

El 05/09/15 a les 14.39, Bob Liu ha escrit:
> Split per ring information to an new structure:xen_blkif_ring, so that one vbd
> device can associate with one or more rings/hardware queues.
> 
> This patch is a preparation for supporting multi hardware queues/rings.
> 
> Signed-off-by: Arianna Avanzini <avanzini.arianna@gmail.com>
> Signed-off-by: Bob Liu <bob.liu@oracle.com>
> ---
>  drivers/block/xen-blkback/blkback.c |  365 ++++++++++++++++++-----------------
>  drivers/block/xen-blkback/common.h  |   52 +++--
>  drivers/block/xen-blkback/xenbus.c  |  130 +++++++------
>  3 files changed, 295 insertions(+), 252 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
> index 954c002..fd02240 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -113,71 +113,71 @@ module_param(log_stats, int, 0644);
>  /* Number of free pages to remove on each call to gnttab_free_pages */
>  #define NUM_BATCH_FREE_PAGES 10
>  
> -static inline int get_free_page(struct xen_blkif *blkif, struct page **page)
> +static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page)
>  {
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&blkif->free_pages_lock, flags);
> -	if (list_empty(&blkif->free_pages)) {
> -		BUG_ON(blkif->free_pages_num != 0);
> -		spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
> +	spin_lock_irqsave(&ring->free_pages_lock, flags);
> +	if (list_empty(&ring->free_pages)) {

I'm afraid the pool of free pages should be per-device, not per-ring.

> +		BUG_ON(ring->free_pages_num != 0);
> +		spin_unlock_irqrestore(&ring->free_pages_lock, flags);
>  		return gnttab_alloc_pages(1, page);
>  	}
> -	BUG_ON(blkif->free_pages_num == 0);
> -	page[0] = list_first_entry(&blkif->free_pages, struct page, lru);
> +	BUG_ON(ring->free_pages_num == 0);
> +	page[0] = list_first_entry(&ring->free_pages, struct page, lru);
>  	list_del(&page[0]->lru);
> -	blkif->free_pages_num--;
> -	spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
> +	ring->free_pages_num--;
> +	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
>  
>  	return 0;
>  }
>  
> -static inline void put_free_pages(struct xen_blkif *blkif, struct page **page,
> +static inline void put_free_pages(struct xen_blkif_ring *ring, struct page **page,
>                                    int num)
>  {
>  	unsigned long flags;
>  	int i;
>  
> -	spin_lock_irqsave(&blkif->free_pages_lock, flags);
> +	spin_lock_irqsave(&ring->free_pages_lock, flags);
>  	for (i = 0; i < num; i++)
> -		list_add(&page[i]->lru, &blkif->free_pages);
> -	blkif->free_pages_num += num;
> -	spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
> +		list_add(&page[i]->lru, &ring->free_pages);
> +	ring->free_pages_num += num;
> +	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
>  }
>  
> -static inline void shrink_free_pagepool(struct xen_blkif *blkif, int num)
> +static inline void shrink_free_pagepool(struct xen_blkif_ring *ring, int num)
>  {
>  	/* Remove requested pages in batches of NUM_BATCH_FREE_PAGES */
>  	struct page *page[NUM_BATCH_FREE_PAGES];
>  	unsigned int num_pages = 0;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&blkif->free_pages_lock, flags);
> -	while (blkif->free_pages_num > num) {
> -		BUG_ON(list_empty(&blkif->free_pages));
> -		page[num_pages] = list_first_entry(&blkif->free_pages,
> +	spin_lock_irqsave(&ring->free_pages_lock, flags);
> +	while (ring->free_pages_num > num) {
> +		BUG_ON(list_empty(&ring->free_pages));
> +		page[num_pages] = list_first_entry(&ring->free_pages,
>  		                                   struct page, lru);
>  		list_del(&page[num_pages]->lru);
> -		blkif->free_pages_num--;
> +		ring->free_pages_num--;
>  		if (++num_pages == NUM_BATCH_FREE_PAGES) {
> -			spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
> +			spin_unlock_irqrestore(&ring->free_pages_lock, flags);
>  			gnttab_free_pages(num_pages, page);
> -			spin_lock_irqsave(&blkif->free_pages_lock, flags);
> +			spin_lock_irqsave(&ring->free_pages_lock, flags);
>  			num_pages = 0;
>  		}
>  	}
> -	spin_unlock_irqrestore(&blkif->free_pages_lock, flags);
> +	spin_unlock_irqrestore(&ring->free_pages_lock, flags);
>  	if (num_pages != 0)
>  		gnttab_free_pages(num_pages, page);
>  }
>  
>  #define vaddr(page) ((unsigned long)pfn_to_kaddr(page_to_pfn(page)))
>  
> -static int do_block_io_op(struct xen_blkif *blkif);
> -static int dispatch_rw_block_io(struct xen_blkif *blkif,
> +static int do_block_io_op(struct xen_blkif_ring *ring);
> +static int dispatch_rw_block_io(struct xen_blkif_ring *ring,
>  				struct blkif_request *req,
>  				struct pending_req *pending_req);
> -static void make_response(struct xen_blkif *blkif, u64 id,
> +static void make_response(struct xen_blkif_ring *ring, u64 id,
>  			  unsigned short op, int st);
>  
>  #define foreach_grant_safe(pos, n, rbtree, node) \
> @@ -198,19 +198,19 @@ static void make_response(struct xen_blkif *blkif, u64 id,
>   * bit operations to modify the flags of a persistent grant and to count
>   * the number of used grants.
>   */
> -static int add_persistent_gnt(struct xen_blkif *blkif,
> +static int add_persistent_gnt(struct xen_blkif_ring *ring,
>  			       struct persistent_gnt *persistent_gnt)
>  {
>  	struct rb_node **new = NULL, *parent = NULL;
>  	struct persistent_gnt *this;
>  
> -	if (blkif->persistent_gnt_c >= xen_blkif_max_pgrants) {
> -		if (!blkif->vbd.overflow_max_grants)
> -			blkif->vbd.overflow_max_grants = 1;
> +	if (ring->persistent_gnt_c >= xen_blkif_max_pgrants) {
> +		if (!ring->blkif->vbd.overflow_max_grants)
> +			ring->blkif->vbd.overflow_max_grants = 1;

The same for the pool of persistent grants, it should be per-device and
not per-ring.

And I think this issue is far worse than the others, because a frontend
might use a persistent grant on different queues, forcing the backend
map the grant several times for each queue, this is not acceptable IMO.

Roger.