[ovs-dev] [PATCH net-next v6 05/10] net: openvswitch: optimize flow-mask looking up

William Tu u9012063 at gmail.com
Mon Nov 4 13:59:27 UTC 2019


On Sat, Nov 2, 2019 at 11:50 PM Pravin Shelar <pshelar at ovn.org> wrote:
>
> On Fri, Nov 1, 2019 at 7:24 AM <xiangxia.m.yue at gmail.com> wrote:
> >
> > From: Tonghao Zhang <xiangxia.m.yue at gmail.com>
> >
> > The full looking up on flow table traverses all mask array.
> > If mask-array is too large, the number of invalid flow-mask
> > increase, performance will be drop.
> >
> > One bad case, for example: M means flow-mask is valid and NULL
> > of flow-mask means deleted.
> >
> > +-------------------------------------------+
> > | M | NULL | ...                  | NULL | M|
> > +-------------------------------------------+
> >
> > In that case, without this patch, openvswitch will traverses all
> > mask array, because there will be one flow-mask in the tail. This
> > patch changes the way of flow-mask inserting and deleting, and the
> > mask array will be keep as below: there is not a NULL hole. In the
> > fast path, we can "break" "for" (not "continue") in flow_lookup
> > when we get a NULL flow-mask.
> >
> >          "break"
> >             v
> > +-------------------------------------------+
> > | M | M |  NULL |...           | NULL | NULL|
> > +-------------------------------------------+
> >
> > This patch don't optimize slow or control path, still using ma->max
> > to traverse. Slow path:
> > * tbl_mask_array_realloc
> > * ovs_flow_tbl_lookup_exact
> > * flow_mask_find
> >
> > Signed-off-by: Tonghao Zhang <xiangxia.m.yue at gmail.com>
> > Tested-by: Greg Rose <gvrose8192 at gmail.com>
> > ---
> Acked-by: Pravin B Shelar <pshelar at ovn.org>

Nack to this patch.

It makes the mask cache invalid when moving the flow mask
to fill another hole.
And the penalty for miss the mask cache is larger than the
benefit of this patch (avoiding the NULL flow-mask).

William


More information about the dev mailing list