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ipv6: Use hash-threshold instead of modulo-N
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Now that each nexthop stores its region boundary in the multipath hash
function's output space, we can use hash-threshold instead of modulo-N
in multipath selection.

This reduces the number of checks we need to perform during lookup, as
dead and linkdown nexthops are assigned a negative region boundary. In
addition, in contrast to modulo-N, only flows near region boundaries are
affected when a nexthop is added or removed.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Ido Schimmel authored and David S. Miller committed Jan 10, 2018
1 parent 7696c06 commit 3d709f6
Showing 1 changed file with 13 additions and 23 deletions.
36 changes: 13 additions & 23 deletions net/ipv6/route.c
Original file line number Diff line number Diff line change
Expand Up @@ -455,36 +455,26 @@ static struct rt6_info *rt6_multipath_select(struct rt6_info *match,
int strict)
{
struct rt6_info *sibling, *next_sibling;
int route_choosen;

/* We might have already computed the hash for ICMPv6 errors. In such
* case it will always be non-zero. Otherwise now is the time to do it.
*/
if (!fl6->mp_hash)
fl6->mp_hash = rt6_multipath_hash(fl6, NULL);

route_choosen = fl6->mp_hash % (match->rt6i_nsiblings + 1);
/* Don't change the route, if route_choosen == 0
* (siblings does not include ourself)
*/
if (route_choosen)
list_for_each_entry_safe(sibling, next_sibling,
&match->rt6i_siblings, rt6i_siblings) {
route_choosen--;
if (route_choosen == 0) {
struct inet6_dev *idev = sibling->rt6i_idev;

if (sibling->rt6i_nh_flags & RTNH_F_DEAD)
break;
if (sibling->rt6i_nh_flags & RTNH_F_LINKDOWN &&
idev->cnf.ignore_routes_with_linkdown)
break;
if (rt6_score_route(sibling, oif, strict) < 0)
break;
match = sibling;
break;
}
}
if (fl6->mp_hash <= atomic_read(&match->rt6i_nh_upper_bound))
return match;

list_for_each_entry_safe(sibling, next_sibling, &match->rt6i_siblings,
rt6i_siblings) {
if (fl6->mp_hash > atomic_read(&sibling->rt6i_nh_upper_bound))
continue;
if (rt6_score_route(sibling, oif, strict) < 0)
break;
match = sibling;
break;
}

return match;
}

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