Re: [dpdk-dev] [PATCH] Minor fixes in rte_common.h file.

[Ravi Kerur <rkerur@gmail.com>]

On Sat, Dec 13, 2014 at 2:39 AM, Neil Horman <nhorman@tuxdriver.com> wrote:
>
> On Fri, Dec 12, 2014 at 03:04:34PM -0800, r k wrote:
> > Subject: [PATCH] Minor fixes in rte_common.h file.
> >
> > Fix rte_is_power_of_2 since 0 is not.
> > Avoid branching instructions in RTE_MAX and RTE_MIN.
> >
> > Signed-off-by: Ravi Kerur <rkerur@gmail.com>
> > ---
> >  lib/librte_eal/common/include/rte_common.h | 6 +++---
> >  lib/librte_pmd_e1000/igb_pf.c              | 4 ++--
> >  lib/librte_pmd_ixgbe/ixgbe_pf.c            | 4 ++--
> >  3 files changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/lib/librte_eal/common/include/rte_common.h
> > b/lib/librte_eal/common/include/rte_common.h
> > index 921b91f..e163f35 100644
> > --- a/lib/librte_eal/common/include/rte_common.h
> > +++ b/lib/librte_eal/common/include/rte_common.h
> > @@ -203,7 +203,7 @@ extern int RTE_BUILD_BUG_ON_detected_error;  static
> > inline int  rte_is_power_of_2(uint32_t n)  {
> > -       return ((n-1) & n) == 0;
> > +       return n && !(n & (n - 1));
> >  }
> >
> >  /**
> > @@ -259,7 +259,7 @@ rte_align64pow2(uint64_t v)  #define RTE_MIN(a, b)
> ({ \
> >                 typeof (a) _a = (a); \
> >                 typeof (b) _b = (b); \
> > -               _a < _b ? _a : _b; \
> > +                _b ^ ((_a ^ _b) & -(_a < _b)); \
> Are you sure this is actually faster than the branch version?  What about
> using
> a cmov instead?
>
>
<rk> i am pretty sure modified code is faster than branching. I remember
cmov had performance issues esp. on Pentuim-4 not sure how new intel cpu's
perform.

>         })
> >
> >  /**
> > @@ -268,7 +268,7 @@ rte_align64pow2(uint64_t v)  #define RTE_MAX(a, b)
> ({ \
> >                 typeof (a) _a = (a); \
> >                 typeof (b) _b = (b); \
> > -               _a > _b ? _a : _b; \
> > +               _a ^ ((_a ^ _b) & -(_a < _b)); \
> Same as above
>
> <rk> Same as above.

> >         })
> >
> >  /*********** Other general functions / macros ********/ diff --git
> > a/lib/librte_pmd_e1000/igb_pf.c b/lib/librte_pmd_e1000/igb_pf.c index
> > bc3816a..546499c 100644
> > --- a/lib/librte_pmd_e1000/igb_pf.c
> > +++ b/lib/librte_pmd_e1000/igb_pf.c
> > @@ -321,11 +321,11 @@ igb_vf_set_mac_addr(struct rte_eth_dev *dev,
> uint32_t
> > vf, uint32_t *msgbuf)  static int  igb_vf_set_multicast(struct
> rte_eth_dev
> > *dev, __rte_unused uint32_t vf, uint32_t *msgbuf)  {
> > -       int i;
> > +       int16_t i;
> >         uint32_t vector_bit;
> >         uint32_t vector_reg;
> >         uint32_t mta_reg;
> > -       int entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >>
> > +       int32_t entries = (msgbuf[0] & E1000_VT_MSGINFO_MASK) >>
> >                 E1000_VT_MSGINFO_SHIFT;
> NAK, this has nothing to do with the included changelog
>

<rk> It does, it causes compilation errors such as

/root/dpdk-new/dpdk/lib/librte_pmd_e1000/igb_pf.c: In function
\u2018igb_pf_mbx_process\u2019:
/root/dpdk-new/dpdk/lib/librte_pmd_e1000/igb_pf.c:350:23: error: array
subscript is above array bounds [-Werror=array-bounds]
   vfinfo->vf_mc_hashes[i] = hash_list[i];
                       ^
cc1: all warnings being treated as errors

Also it is always better to use explicit int definitions esp. for 64bit
systems.



>
> >         uint16_t *hash_list = (uint16_t *)&msgbuf[1];
> >         struct e1000_hw *hw =
> > E1000_DEV_PRIVATE_TO_HW(dev->data->dev_private);
> > diff --git a/lib/librte_pmd_ixgbe/ixgbe_pf.c
> > b/lib/librte_pmd_ixgbe/ixgbe_pf.c index 51da1fd..426caf9 100644
> > --- a/lib/librte_pmd_ixgbe/ixgbe_pf.c
> > +++ b/lib/librte_pmd_ixgbe/ixgbe_pf.c
> > @@ -390,7 +390,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev,
> > __rte_unused uint32_t vf, uint32
> >         struct ixgbe_hw *hw =
> > IXGBE_DEV_PRIVATE_TO_HW(dev->data->dev_private);
> >         struct ixgbe_vf_info *vfinfo =
> >                 *(IXGBE_DEV_PRIVATE_TO_P_VFDATA(dev->data->dev_private));
> > -       int nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >>
> > +       int32_t nb_entries = (msgbuf[0] & IXGBE_VT_MSGINFO_MASK) >>
> >                 IXGBE_VT_MSGINFO_SHIFT;
> ditto
> >         uint16_t *hash_list = (uint16_t *)&msgbuf[1];
> >         uint32_t mta_idx;
> > @@ -399,7 +399,7 @@ ixgbe_vf_set_multicast(struct rte_eth_dev *dev,
> > __rte_unused uint32_t vf, uint32
> >         const uint32_t IXGBE_MTA_BIT_SHIFT = 5;
> >         const uint32_t IXGBE_MTA_BIT_MASK = (0x1 << IXGBE_MTA_BIT_SHIFT)
> -
> > 1;
> >         uint32_t reg_val;
> > -       int i;
> > +       int16_t i;
> ditto
>
> <rk> Same as above.

> >
> >         /* only so many hash values supported */
> >         nb_entries = RTE_MIN(nb_entries, IXGBE_MAX_VF_MC_ENTRIES);
> > --
> > 1.9.1
> >
>