Re: [dpdk-dev] [PATCH v2] net/ixgbevf: update VF_STAT macros to handle rollover

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 1/26/2020 5:32 PM, David Harton wrote:
> Added rollover logic to UPDATE_VF_STAT and UPDATE_VF_STAT_36BIT macros.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: intel.com
> 
> Signed-off-by: David Harton <dharton@cisco.com>
> ---
>  drivers/net/ixgbe/ixgbe_ethdev.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c b/drivers/net/ixgbe/ixgbe_ethdev.c
> index 49285ce53..bc73ad195 100644
> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
> @@ -385,7 +385,11 @@ static void ixgbe_l2_tunnel_conf(struct rte_eth_dev *dev);
>  #define UPDATE_VF_STAT(reg, last, cur)                          \
>  {                                                               \
>  	uint32_t latest = IXGBE_READ_REG(hw, reg);              \
> -	cur += (latest - last) & UINT_MAX;                      \

Here since 'last' is 'u64', the 'UINT_MAX' is required, but overall this looks
good, original code should be OK.

> +	if (latest >= last)                                     \
> +		cur += (latest - last);                         \
> +	else                                                    \
> +		cur += ((latest + ((uint64_t)1 << 32)) - last); \
> +	cur &= UINT_MAX;                                        \
>  	last = latest;                                          \
>  }
>  
> @@ -394,7 +398,11 @@ static void ixgbe_l2_tunnel_conf(struct rte_eth_dev *dev);
>  	u64 new_lsb = IXGBE_READ_REG(hw, lsb);                   \
>  	u64 new_msb = IXGBE_READ_REG(hw, msb);                   \
>  	u64 latest = ((new_msb << 32) | new_lsb);                \
> -	cur += (0x1000000000LL + latest - last) & 0xFFFFFFFFFLL; \
> +	if (latest >= last)                                      \
> +		cur += (latest - last);                          \
> +	else                                                     \
> +		cur += ((latest + ((u64)1 << 36)) - last);       \
> +	cur &= 0xFFFFFFFFFLL;                                    \

For this case old and new implementation looks same to me.

>  	last = latest;                                           \
>  }
>  
>