Re: [PATCH v4 24/40] RDMA/rtrs: optimize __rtrs_get_permit() by using find_and_set_bit_lock()

[Jinpu Wang]

On Thu, Jun 20, 2024 at 7:58 PM Yury Norov <yury.norov@xxxxxxxxx> wrote:
>
> The function opencodes find_and_set_bit_lock() with a while-loop polling
> on test_and_set_bit_lock(). Use the dedicated function instead.
>
> Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
lgtm, thx!
Reviewed-by: Jack Wang <jinpu.wang@xxxxxxxxx>
> ---
>  drivers/infiniband/ulp/rtrs/rtrs-clt.c | 16 ++++------------
>  1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/infiniband/ulp/rtrs/rtrs-clt.c b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> index 88106cf5ce55..52b7728f6c63 100644
> --- a/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> +++ b/drivers/infiniband/ulp/rtrs/rtrs-clt.c
> @@ -10,6 +10,7 @@
>  #undef pr_fmt
>  #define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
>
> +#include <linux/find_atomic.h>
>  #include <linux/module.h>
>  #include <linux/rculist.h>
>  #include <linux/random.h>
> @@ -72,18 +73,9 @@ __rtrs_get_permit(struct rtrs_clt_sess *clt, enum rtrs_clt_con_type con_type)
>         struct rtrs_permit *permit;
>         int bit;
>
> -       /*
> -        * Adapted from null_blk get_tag(). Callers from different cpus may
> -        * grab the same bit, since find_first_zero_bit is not atomic.
> -        * But then the test_and_set_bit_lock will fail for all the
> -        * callers but one, so that they will loop again.
> -        * This way an explicit spinlock is not required.
> -        */
> -       do {
> -               bit = find_first_zero_bit(clt->permits_map, max_depth);
> -               if (bit >= max_depth)
> -                       return NULL;
> -       } while (test_and_set_bit_lock(bit, clt->permits_map));
> +       bit = find_and_set_bit_lock(clt->permits_map, max_depth);
> +       if (bit >= max_depth)
> +               return NULL;
>
>         permit = get_permit(clt, bit);
>         WARN_ON(permit->mem_id != bit);
> --
> 2.43.0
>