Re: [PATCH rdma-next v2 1/4] IB/mlx5: Introduce ODP diagnostic counters

[Jason Gunthorpe <jgg@mellanox.com>]

On Sun, Oct 06, 2019 at 06:51:36PM +0300, Leon Romanovsky wrote:
> From: Erez Alfasi <ereza@mellanox.com>
> 
> Introduce ODP diagnostic counters and count the following
> per MR within IB/mlx5 driver:
>  1) Page faults:
> 	Total number of faulted pages.
>  2) Page invalidations:
> 	Total number of pages invalidated by the OS during all
> 	invalidation events. The translations can be no longer
> 	valid due to either non-present pages or mapping changes.
>  3) Prefetched pages:
> 	When prefetching a page, page fault is generated
> 	in order to bring the page to the main memory.
> 	The prefetched pages counter will be updated
> 	during a page fault flow only if it was derived
> 	from prefetching operation.
> 
> Signed-off-by: Erez Alfasi <ereza@mellanox.com>
> Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
>  drivers/infiniband/hw/mlx5/mlx5_ib.h |  4 ++++
>  drivers/infiniband/hw/mlx5/odp.c     | 18 ++++++++++++++++++
>  include/rdma/ib_verbs.h              |  6 ++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> index bf30d53d94dc..5aae05ebf64b 100644
> +++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> @@ -585,6 +585,9 @@ struct mlx5_ib_dm {
>  					  IB_ACCESS_REMOTE_READ   |\
>  					  IB_ZERO_BASED)
>  
> +#define mlx5_update_odp_stats(mr, counter_name, value)		\
> +	atomic64_add(value, &((mr)->odp_stats.counter_name))
> +
>  struct mlx5_ib_mr {
>  	struct ib_mr		ibmr;
>  	void			*descs;
> @@ -622,6 +625,7 @@ struct mlx5_ib_mr {
>  	wait_queue_head_t       q_leaf_free;
>  	struct mlx5_async_work  cb_work;
>  	atomic_t		num_pending_prefetch;
> +	struct ib_odp_counters	odp_stats;
>  };
>  
>  static inline bool is_odp_mr(struct mlx5_ib_mr *mr)
> diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
> index 95cf0249b015..966783bfb557 100644
> +++ b/drivers/infiniband/hw/mlx5/odp.c
> @@ -261,6 +261,10 @@ void mlx5_ib_invalidate_range(struct ib_umem_odp *umem_odp, unsigned long start,
>  				blk_start_idx = idx;
>  				in_block = 1;
>  			}
> +
> +			/* Count page invalidations */
> +			mlx5_update_odp_stats(mr, invalidations,
> +					      (idx - blk_start_idx + 1));

I feel like these should be batched and the atomic done once at the
end of the routine..

>  		} else {
>  			u64 umr_offset = idx & umr_block_mask;
>  
> @@ -287,6 +291,7 @@ void mlx5_ib_invalidate_range(struct ib_umem_odp *umem_odp, unsigned long start,
>  
>  	ib_umem_odp_unmap_dma_pages(umem_odp, start, end);
>  
> +
>  	if (unlikely(!umem_odp->npages && mr->parent &&
>  		     !umem_odp->dying)) {
>  		WRITE_ONCE(umem_odp->dying, 1);
> @@ -801,6 +806,19 @@ static int pagefault_single_data_segment(struct mlx5_ib_dev *dev,
>  		if (ret < 0)
>  			goto srcu_unlock;
>  
> +		/*
> +		 * When prefetching a page, page fault is generated
> +		 * in order to bring the page to the main memory.
> +		 * In the current flow, page faults are being counted.
> +		 * Prefetched pages counter will be updated as well
> +		 * only if the current page fault flow was derived
> +		 * from prefetching flow.
> +		 */
> +		mlx5_update_odp_stats(mr, faults, ret);
> +
> +		if (prefetch)
> +			mlx5_update_odp_stats(mr, prefetched, ret);

Hm, I'm about to post a series that eliminates 'prefetch' here..

This is also not quite right for prefetch as we are doing a form of
prefetching in the mlx5_ib_mr_rdma_pfault_handler() too, although it
is less clear how to count those. Maybe this should be split to SQ/RQ
faults?

Jason