On Wed, 2018-03-14 at 19:57 -0700, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> The mlx5 driver calls ida_pre_get() in a loop for no readily apparent
> reason. The driver uses ida_simple_get() which will call
> ida_pre_get()
> by itself and there's no need to use ida_pre_get() unless using
> ida_get_new().
>
Hi Matthew,
Is this is causing any issues ? or just a simple cleanup ?
Adding Maor, the author of this change,
I believe the idea is to speed up insert_fte (which calls
ida_simple_get) since insert_fte runs under the FTE write semaphore,
in this case if ida_pre_get was successful before taking the semaphore
for all the FTE nodes in the loop, this will be a huge win for
ida_simple_get which will immediately return success without even
trying to allocate.
so it is a best effort to speed up critical path.
Maor, if this is really the case and this is not causing any issues,
then we need to consider adding a comment.
> Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.c
> b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.c
> index 10e16381f20a..3ba07c7096ef 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/fs_core.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/fs_core.c
> @@ -1647,7 +1647,6 @@ try_add_to_existing_fg(struct mlx5_flow_table
> *ft,
>
> list_for_each_entry(iter, match_head, list) {
> nested_down_read_ref_node(&iter->g->node,
> FS_LOCK_PARENT);
> - ida_pre_get(&iter->g->fte_allocator, GFP_KERNEL);
> }
>
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