Re: [PATCHv2 for-next 13/19] RDMA/rtrs-srv: Replace atomic_t with percpu_ref for ids_inflight

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, May 17, 2021 at 11:18:37AM +0200, Gioh Kim wrote:
> From: Md Haris Iqbal <haris.iqbal@cloud.ionos.com>
> 
> ids_inflight is used to track the inflight IOs. But the use of atomic_t
> variable can cause performance drops and can also become a performance
> bottleneck.
> 
> This commit replaces the use of atomic_t with a percpu_ref structure. The
> advantage it offers is, it doesn't check if the reference has fallen to 0,
> until the user explicitly signals it to; and that is done by the
> percpu_ref_kill() function call. After that, the percpu_ref structure
> behaves like an atomic_t and for every put call, checks whether the
> reference has fallen to 0 or not.
> 
> rtrs_srv_stats_rdma_to_str shows the count of ids_inflight as 0
> for user-mode tools not to be confused.
> 
> Fixes: 9cb837480424e ("RDMA/rtrs: server: main functionality")
> Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
> Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
> Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
> ---
>  drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c | 12 +++---
>  drivers/infiniband/ulp/rtrs/rtrs-srv.c       | 43 +++++++++++++-------
>  drivers/infiniband/ulp/rtrs/rtrs-srv.h       |  4 +-
>  3 files changed, 35 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c b/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
> index e102b1368d0c..df1d7d6b1884 100644
> --- a/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
> +++ b/drivers/infiniband/ulp/rtrs/rtrs-srv-stats.c
> @@ -27,12 +27,10 @@ ssize_t rtrs_srv_stats_rdma_to_str(struct rtrs_srv_stats *stats,
>  				    char *page, size_t len)
>  {
>  	struct rtrs_srv_stats_rdma_stats *r = &stats->rdma_stats;
> -	struct rtrs_srv_sess *sess = stats->sess;
>  
> -	return scnprintf(page, len, "%lld %lld %lld %lld %u\n",
> -			 (s64)atomic64_read(&r->dir[READ].cnt),
> -			 (s64)atomic64_read(&r->dir[READ].size_total),
> -			 (s64)atomic64_read(&r->dir[WRITE].cnt),
> -			 (s64)atomic64_read(&r->dir[WRITE].size_total),
> -			 atomic_read(&sess->ids_inflight));
> +	return sysfs_emit(page, "%lld %lld %lld %lldn\n",
> +			  (s64)atomic64_read(&r->dir[READ].cnt),
> +			  (s64)atomic64_read(&r->dir[READ].size_total),
> +			  (s64)atomic64_read(&r->dir[WRITE].cnt),
> +			  (s64)atomic64_read(&r->dir[WRITE].size_total));
>  }

This seems like an unrelated hunk

Jason