Re: [dpdk-dev] [PATCH] drivers: cleanup unnecessary global variables

[Olivier Matz <olivier.matz@6wind.com>]

On Fri, Apr 20, 2018 at 12:21:59AM +0530, Pavan Nikhilesh wrote:
> Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
> ---
>  drivers/bus/dpaa/base/fman/netcfg_layer.c     | 5 -----
>  drivers/bus/dpaa/base/qbman/bman_driver.c     | 4 ++--
>  drivers/bus/dpaa/base/qbman/qman.c            | 2 +-
>  drivers/bus/dpaa/base/qbman/qman_driver.c     | 4 ++--
>  drivers/bus/dpaa/base/qbman/qman_priv.h       | 1 -
>  drivers/bus/dpaa/dpaa_bus.c                   | 2 +-
>  drivers/bus/fslmc/qbman/qbman_portal.c        | 3 +--
>  drivers/bus/fslmc/qbman/qbman_portal.h        | 1 -
>  drivers/net/i40e/i40e_flow.c                  | 2 +-
>  drivers/net/qede/base/bcm_osal.c              | 2 +-
>  drivers/raw/skeleton_rawdev/skeleton_rawdev.c | 2 +-
>  lib/librte_net/net_crc_neon.h                 | 4 ++--
>  12 files changed, 12 insertions(+), 20 deletions(-)

[...]

> diff --git a/lib/librte_net/net_crc_neon.h b/lib/librte_net/net_crc_neon.h
> index 63fa1d4a1..cb3da72ed 100644
> --- a/lib/librte_net/net_crc_neon.h
> +++ b/lib/librte_net/net_crc_neon.h
> @@ -21,8 +21,8 @@ struct crc_pmull_ctx {
>  	uint64x2_t rk7_rk8;
>  };
>  
> -struct crc_pmull_ctx crc32_eth_pmull __rte_aligned(16);
> -struct crc_pmull_ctx crc16_ccitt_pmull __rte_aligned(16);
> +static struct crc_pmull_ctx crc32_eth_pmull __rte_aligned(16);
> +static struct crc_pmull_ctx crc16_ccitt_pmull __rte_aligned(16);
>  
>  /**

Not sure it will still work after that.

>From what I see, these global variables are initialized once in
rte_net_crc_neon_init, and used as a const parameter in
crc32_eth_calc_pmull().

Changing them to static will create an instance of these variables for
each included file, which is not what we want.

I think that the proper way to solve it would be to add the definition
in a new .c file, and only have a declaration in the .h.


An even better way would be to make variable const and initialize it
with its content. It could even enhance performance. Something like:

net_crc_neon.h:

static const struct crc_pmull_ctx crc32_eth_pmull = {
      <values...>
} __rte_aligned(16);

static const struct crc_pmull_ctx crc16_ccitt_pmull = {
      <values...>
} __rte_aligned(16);