[ovs-dev] [PATCH] reciprocal-divide: Downstream the reciprocal_div.{c, h}.

[Alex Wang]

Thanks Pravin for the review~,


make  all-recursive
> make[1]: Entering directory `/home/pravin/ovs/openvswitch'
> Making all in datapath
> make[2]: Entering directory `/home/pravin/ovs/openvswitch/datapath'
> Making all in linux
> make[3]: Entering directory `/home/pravin/ovs/openvswitch/datapath/linux'
> make -C /lib/modules/2.6.32-358.123.2.openstack.el6.x86_64/build/
> M=/home/pravin/ovs/openvswitch/datapath/linux modules
> make[4]: Entering directory
> `/home/pravin/linux/linux-2.6.32-358.123.2.openstack.el6.x86_64'
>   CC [M]  /home/pravin/ovs/openvswitch/datapath/linux/actions.o
> In file included from
> /home/pravin/ovs/openvswitch/datapath/linux/../flow.h:33,
>                  from
> /home/pravin/ovs/openvswitch/datapath/linux/../datapath.h:30,
>                  from
> /home/pravin/ovs/openvswitch/datapath/linux/actions.c:37:
>
> /home/pravin/ovs/openvswitch/datapath/linux/compat/include/linux/flex_array.h:30:
> error: field 'reciprocal_elems' has incomplete type



Fixed,



> > @@ -94,7 +94,7 @@ struct flex_array *flex_array_alloc(int element_size,
> unsigned int total,
> >  {
> >         struct flex_array *ret;
> >         int elems_per_part = 0;
> > -       int reciprocal_elems = 0;
> > +       struct reciprocal_value reciprocal_elems = 0;
> >         int max_size = 0;
> >
> Use {} to set zero to struct.
>



Thanks, will use it.




> > diff --git a/datapath/linux/compat/include/linux/reciprocal_div.h
> b/datapath/linux/compat/include/linux/reciprocal_div.h
> > new file mode 100644
> > index 0000000..15d40db
> > --- /dev/null
> > +++ b/datapath/linux/compat/include/linux/reciprocal_div.h
> > @@ -0,0 +1,37 @@
> > +#ifndef _LINUX_RECIPROCAL_DIV_H
> > +#define _LINUX_RECIPROCAL_DIV_H
> > +
> This constant should have WRAPPER as suffix so that we can include
> reciprocal_div.h
> if available.



Fixed it,




>  * This algorithm is based on the paper "Division by Invariant
> > + * Integers Using Multiplication" by Torbjörn Granlund and Peter
> > + * L. Montgomery.
> > + *
> > + * The assembler implementation from Agner Fog, which this code is
> > + * based on, can be found here:
> > + * http://www.agner.org/optimize/asmlib.zip
> > + *
> > + * This optimization for A/B is helpful if the divisor B is mostly
> > + * runtime invariant. The reciprocal of B is calculated in the
> > + * slow-path with reciprocal_value(). The fast-path can then just use
> > + * a much faster multiplication operation with a variable dividend A
> > + * to calculate the division A/B.
> > + */
> > +
> Include reciprocal_div.h if available.



Fixed,



> > +struct reciprocal_value reciprocal_value(u32 d)
> >  {
> > -       u64 val = (1LL << 32) + (k - 1);
> > -       do_div(val, k);
> > -       return (u32)val;
> > +       struct reciprocal_value R;
> > +       u64 m;
> > +       int l;
> > +
> > +       l = fls(d - 1);
> > +       m = ((1ULL << 32) * ((1ULL << l) - d));
> > +       do_div(m, d);
> > +       ++m;
> > +       R.m = (u32)m;
> > +       R.sh1 = min(l, 1);
> > +       R.sh2 = max(l - 1, 0);
> > +
> > +       return R;
> >  }
> > -#endif
> > +EXPORT_SYMBOL(reciprocal_value);
>
> Why are you exporting this symbol?
>

I'll remove this line.
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