Re: [PATCH] Minor fixes in rte_common.h file.

[Neil Horman <nhorman-2XuSBdqkA4R54TAoqtyWWQ@public.gmane.org>]

On Fri, Dec 12, 2014 at 03:04:34PM -0800, r k wrote:
> Subject: [PATCH] Minor fixes in rte_common.h file.
> 
> Fix rte_is_power_of_2 since 0 is not.
> Avoid branching instructions in RTE_MAX and RTE_MIN.
> 
> Signed-off-by: Ravi Kerur <rkerur-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  lib/librte_eal/common/include/rte_common.h | 6 +++---
>  lib/librte_pmd_e1000/igb_pf.c              | 4 ++--
>  lib/librte_pmd_ixgbe/ixgbe_pf.c            | 4 ++--
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_common.h
> b/lib/librte_eal/common/include/rte_common.h
> index 921b91f..e163f35 100644
> --- a/lib/librte_eal/common/include/rte_common.h
> +++ b/lib/librte_eal/common/include/rte_common.h
> @@ -203,7 +203,7 @@ extern int RTE_BUILD_BUG_ON_detected_error;  static
> inline int  rte_is_power_of_2(uint32_t n)  {
> -       return ((n-1) & n) == 0;
> +       return n && !(n & (n - 1));
>  }
> 
>  /**
> @@ -259,7 +259,7 @@ rte_align64pow2(uint64_t v)  #define RTE_MIN(a, b) ({ \
>                 typeof (a) _a = (a); \
>                 typeof (b) _b = (b); \
> -               _a < _b ? _a : _b; \
> +                _b ^ ((_a ^ _b) & -(_a < _b)); \
Are you sure this is actually faster than the branch version?  What about using
a cmov instead?

>         })
> 
>  /**
> @@ -268,7 +268,7 @@ rte_align64pow2(uint64_t v)  #define RTE_MAX(a, b) ({ \
>                 typeof (a) _a = (a); \
>                 typeof (b) _b = (b); \
> -               _a > _b ? _a : _b; \
> +               _a ^ ((_a ^ _b) & -(_a < _b)); \
Same as above

>         })
> 
>  /*********** Other general functions / macros ********/ diff --git
> a/lib/librte_pmd_e1000/igb_pf.c b/lib/librte_pmd_e1000/igb_pf.c index
> bc3816a..546499c 100644
> --- a/lib/librte_pmd_e1000/igb_pf.c
> +++ b/lib/librte_pmd_e1000/igb_pf.c
> @@ -321,11 +321,11 @@ igb_vf_set_mac_addr(struct rte_eth_dev *dev, uint32_t
> vf, uint32_t *msgbuf)  static int  igb_vf_set_multicast(struct rte_eth_dev
> *dev, __rte_unused uint32_t vf, uint32_t *msgbuf)  {
> -       int i;
> +       int16_t i;
>         uint32_t vector_bit;
>         uint32_t vector_reg;
>         uint32_t mta_reg;
> -       int entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >>
> +       int32_t entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >>
>                 E1000_VT_MSGINFO_SHIFT;
NAK, this has nothing to do with the included changelog

>         uint16_t *hash_list = (uint16_t *)&msgbuf[1];
>         struct e1000_hw *hw =
> E1000_DEV_PRIVATE_TO_HW(dev->data->dev_private);
> diff --git a/lib/librte_pmd_ixgbe/ixgbe_pf.c
> b/lib/librte_pmd_ixgbe/ixgbe_pf.c index 51da1fd..426caf9 100644
> --- a/lib/librte_pmd_ixgbe/ixgbe_pf.c
> +++ b/lib/librte_pmd_ixgbe/ixgbe_pf.c
> @@ -390,7 +390,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev,
> __rte_unused uint32_t vf, uint32
>         struct ixgbe_hw *hw =
> IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
>         struct ixgbe_vf_info *vfinfo =
>                 *(IXGBE_DEV_PRIVATE_TO_P_VFDATA(dev->data->dev_private));
> -       int nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >>
> +       int32_t nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >>
>                 IXGBE_VT_MSGINFO_SHIFT;
ditto
>         uint16_t *hash_list = (uint16_t *)&msgbuf[1];
>         uint32_t mta_idx;
> @@ -399,7 +399,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev,
> __rte_unused uint32_t vf, uint32
>         const uint32_t IXGBE_MTA_BIT_SHIFT = 5;
>         const uint32_t IXGBE_MTA_BIT_MASK = (0x1 << IXGBE_MTA_BIT_SHIFT) -
> 1;
>         uint32_t reg_val;
> -       int i;
> +       int16_t i;
ditto

> 
>         /* only so many hash values supported */
>         nb_entries = RTE_MIN(nb_entries, IXGBE_MAX_VF_MC_ENTRIES);
> --
> 1.9.1
>