Re: [PATCH v3] Fix one error in mthca_alloc

[Leon Romanovsky <leon@kernel.org>]

On Fri, Aug 27, 2021 at 08:52:28AM +0800, kangning wrote:
> drivers/infiniband/hw/mthca/mthca_allocator.c: alloc->last left unchanged in mthca_alloc, which
> has impact on performance of function find_next_zero_bit in mthca_alloc.

I don't know what the sentence above means, but the change is unlikely
to be correct.

When alloc->last starts to be equal to alloc->max, the
find_next_zero_bit() will always return alloc->max. which will ensure
that the following code is executed.

   48         if (obj >= alloc->max) {
   49                 alloc->top = (alloc->top + alloc->max) & alloc->mask;
   50                 obj = find_first_zero_bit(alloc->table, alloc->max);
   51         }


However the mthca_alloc() function has other error, it returns -1 while
based on its declaration it needs to be unsigned,

Thanks

> 
> Signed-off-by: kangning <kangning18z@ict.ac.cn>
> ---
>  
>  I squashed two commits into one in this version.
>  
>  drivers/infiniband/hw/mthca/mthca_allocator.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/infiniband/hw/mthca/mthca_allocator.c b/drivers/infiniband/hw/mthca/mthca_allocator.c
> index aef1d274a14e..1141695093e7 100644
> --- a/drivers/infiniband/hw/mthca/mthca_allocator.c
> +++ b/drivers/infiniband/hw/mthca/mthca_allocator.c
> @@ -51,6 +51,9 @@ u32 mthca_alloc(struct mthca_alloc *alloc)
>  	}
>  
>  	if (obj < alloc->max) {
> +		alloc->last = obj + 1;
> +		if (alloc->last == alloc->max)
> +			alloc->last = 0;
>  		set_bit(obj, alloc->table);
>  		obj |= alloc->top;
>  	} else
> -- 
> 2.17.1
>