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

["David Harton (dharton)" <dharton@cisco.com>]

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Wednesday, January 29, 2020 6:23 AM
> To: David Harton (dharton) <dharton@cisco.com>; dev@dpdk.org
> Cc: wenzhuo.lu@intel.com; konstantin.ananyev@intel.com;
> xiaolong.ye@intel.com; intel.com@cisco.com
> Subject: Re: [dpdk-dev] [PATCH v2] net/ixgbevf: update VF_STAT macros to
> handle rollover
> 
> 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.

Agreed.  As mentioned on the igbvf thread I've gone back to the developer for justification.

Regards,
Dave

> 
> > +	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;                                           \
> >  }
> >
> >