On Mon, Nov 4, 2019 at 6:00 AM William Tu [off-list ref] wrote:

On Sat, Nov 2, 2019 at 11:50 PM Pravin Shelar [off-list ref] wrote:

quoted

On Fri, Nov 1, 2019 at 7:24 AM [off-list ref] wrote:

quoted

From: Tonghao Zhang <redacted>

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 <redacted>
Tested-by: Greg Rose <redacted>
---

Acked-by: Pravin B Shelar <redacted>

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).

Hi William,

The cache invalidation would occur in case of changes to flow mask
list. I think in general datapath processing there should not be too
many changes to mask list since a mask is typically shared between
multiple mega flows. Flow-table changes does not always result in mask
list updates. In last round Tonghao has posted number to to support
this patch.
If you are worried about some other use case can you provide
performance numbers, that way we can take this discussion forward.

Thanks,
Pravin.