[dpdk-dev] [PATCH 1/2] ixgbe: fix VF statistic wraparound handling macro
Roger B. Melton
rmelton at cisco.com
Tue Oct 13 21:43:33 CEST 2015
Agreed, this handles the off by one error on wrap around and should be
faster.
-Roger
On 10/12/15 11:41 AM, Alexander Duyck wrote:
> 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
> .
>
--
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