From: "Roger B. Melton" <rmelton@cisco.com>
To: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 1/2] ixgbe: fix VF statistic wraparound handling macro
Date: Tue, 13 Oct 2015 15:43:33 -0400 [thread overview]
Message-ID: <561D5EE5.2000507@cisco.com> (raw)
In-Reply-To: <561BD4AE.4010704@gmail.com>
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@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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next prev parent reply other threads:[~2015-10-13 19:43 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-12 13:33 [dpdk-dev] [PATCH 0/2] fix vf statistic wraparound handling in macro Harry van Haaren
2015-10-12 13:33 ` [dpdk-dev] [PATCH 1/2] ixgbe: fix VF statistic wraparound handling macro Harry van Haaren
2015-10-12 14:45 ` Roger B. Melton
2015-10-12 15:41 ` Alexander Duyck
2015-10-12 16:45 ` [dpdk-dev] [PATCH 0/2] fix vf statistic wraparound handling in macro Harry van Haaren
2015-10-12 16:45 ` [dpdk-dev] [PATCH 1/2] ixgbe: fix VF statistic wraparound handling macro Harry van Haaren
2015-10-13 19:43 ` Roger B. Melton
2015-10-14 10:15 ` Roger B. Melton
2015-10-28 13:37 ` Thomas Monjalon
2015-10-12 16:45 ` [dpdk-dev] [PATCH 2/2] igb: " Harry van Haaren
2015-10-13 19:44 ` Roger B. Melton
2015-10-14 10:16 ` Roger B. Melton
2015-10-28 13:40 ` [dpdk-dev] [PATCH 0/2] fix vf statistic wraparound handling in macro Thomas Monjalon
2015-10-13 19:43 ` Roger B. Melton [this message]
2015-10-12 13:33 ` [dpdk-dev] [PATCH 2/2] igb: fix VF statistic wraparound handling macro Harry van Haaren
2015-10-12 15:02 ` Roger B. Melton
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