Re: [dpdk-dev] [PATCH] Add toeplitz hash algorithm

[Vladimir Medvedkin <medvedkinv@gmail.com>]

Hi Stephen,



2015-04-09 1:24 GMT+03:00 Stephen Hemminger <stephen@networkplumber.org>:

> On Wed,  8 Apr 2015 15:06:13 -0400
> Vladimir Medvedkin <medvedkinv@gmail.com> wrote:
>
> > Software implementation of the Toeplitz hash function used by RSS.
> > Can be used either for packet distribution on single queue NIC
> > or for simulating of RSS computation on specific NIC (for example
> > after GRE header decapsulating).
> >
> > Signed-off-by: Vladimir Medvedkin <medvedkinv@gmail.com>
>
> > +enum rte_thash_flag {
> > +     RTE_THASH_L3 = 0,       //calculate hash tacking into account only
> l3 header
> > +     RTE_THASH_L4            //calculate hash tacking into account l4 +
> l4 headers
> > +};
> > +
> > +/**
> > + * Prepare special converted key to use with rte_softrss_be()
> > + * @param orig
> > + *   pointer to original RSS key
> > + * @param targ
> > + *   pointer to target RSS key
> > + */
> > +
> > +static inline void
> > +rte_convert_rss_key(uint32_t *orig, uint32_t *targ)
> orig should be const
>
> > +{
> > +     int i;
> > +     for (i = 0; i < 10; i++) {
> > +             targ[i] = rte_be_to_cpu_32(orig[i]);
> > +     }
> > +}
>
> > +static inline uint32_t
> > +rte_softrss(uint32_t sip, uint32_t dip, uint16_t sp, uint16_t dp, enum
> rte_thash_flag flag, uint32_t *rss_key)
>
> rss_key should be const
>
> > +{
> > +     uint32_t ret = 0;
> > +     int i;
> > +     for (i = 0; i < 32; i++) {
> blank line after declaration please
>
> > +             if (sip & (1 << (31 - i))) {
> > +                     ret ^= (rte_cpu_to_be_32(*rss_key) <<
> i)|(uint32_t)((uint64_t)(rte_cpu_to_be_32(*(rss_key + 1))) >> (32 - i));
>
> Long expression > 80 characters.
> Repeated multiple times (should be inline)
> Extra parens ()
>
Thanks for remarks, I'll fix it.

> Extension to 64 bits is only to avoid compiler warning?
>
No, in case when i = 0 we shift uint32_t left by 32 bits, which leads to
undefined behaviour. In fact, shift counter just masked to 5 bits, so count
range is limited to 0 to 31.

>
>
> > +             }
> > +     }
> > +     rss_key++;
> > +     for (i = 0; i < 32; i++) {
> > +             if (dip & (1 << (31 - i))) {
> > +                     ret ^= (rte_cpu_to_be_32(*rss_key) <<
> i)|(uint32_t)((uint64_t)(rte_cpu_to_be_32(*(rss_key + 1))) >> (32 - i));
> > +             }
> > +     }
> > +        if (flag == RTE_THASH_L4) {
> > +             rss_key++;
> > +             for (i = 0; i < 32; i++) {
> > +                     if (((sp<<16)|dp) & (1 << (31 - i))) {
> > +                             ret ^= (rte_cpu_to_be_32(*rss_key) <<
> i)|(uint32_t)((uint64_t)(rte_cpu_to_be_32(*(rss_key + 1))) >> (32 - i));
> > +                     }
> > +             }
> > +     }
> > +     return ret;
> > +}
> > +
> > +/**
> > + * Optimized implementation.
> > + * If you want the calculated hash value matches NIC RSS value
> > + * you have to use special converted key.
> > + * All ip's and ports have to be CPU byte order.
> > + * @param sip
> > + *   Source ip address.
> > + * @param dip
> > + *   Destination ip address.
> > + * @param sp
> > + *   Source TCP|UDP port.
> > + * @param dp
> > + *   Destination TCP|UDP port.
> > + * @param flag
> > + *   RTE_THASH_L3:   calculate hash tacking into account only sip and
> dip
> > + *   RTE_THASH_L4:   calculate hash tacking into account sip, dip, sp
> and dp
> > + * @param *rss_key
> > + *   Pointer to 40-byte RSS hash key.
> > + * @return
> > + *   Calculated hash value.
> > + */
> > +
> > +static inline uint32_t
> > +rte_softrss_be(uint32_t sip, uint32_t dip, uint16_t sp, uint16_t dp,
> enum rte_thash_flag flag, uint32_t *rss_key)
> > +{
>
> Same problems as previous code.
> Also lots of copy paste (see Do Not Repeat Yourself principle).
>