On 10/12/2015 06:33 AM, Harry van Haaren wrote:
> Fix a misinterpretation of VF stats in ixgbe
>
> Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
> ---
> drivers/net/ixgbe/ixgbe_ethdev.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c
> b/drivers/net/ixgbe/ixgbe_ethdev.c
> index ec2918c..d226e8d 100644
> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
> @@ -329,10 +329,14 @@ static int ixgbe_timesync_read_tx_timestamp(struct
> rte_eth_dev *dev,
> /*
> * Define VF Stats MACRO for Non "cleared on read" register
> */
> -#define UPDATE_VF_STAT(reg, last, cur) \
> +#define UPDATE_VF_STAT(reg, last, cur) \
> { \
> uint32_t latest = IXGBE_READ_REG(hw, reg); \
> - cur += latest - last; \
> + if(likely(latest > last)) { \
> + cur += latest - last; \
> + } else { \
> + cur += (UINT_MAX - last) + latest; \
> + } \
> last = latest; \
> }
>
From what I can tell your math is adding an off by one error. You
should probably be using UINT_MAX as a mask for the result, not as a
part of the calculation itself.
So the correct way to compute this would be "cur += (latest - last) &
UINT_MAX". Also the mask approach should be faster as it avoids any
conditional jumps.
- Alex
