On Wed, Oct 2, 2019 at 10:03 AM Pravin Shelar [off-list ref] wrote:

On Sun, Sep 29, 2019 at 7:09 PM [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.

This patch optimizes mask-array operation:

* Inserting, insert it [ma->count- 1] directly.
* Removing, only change last and current mask point, and free current mask.
* Looking up, full looking up will break if mask is NULL.

The function which changes or gets *count* of struct mask_array,
is protected by ovs_lock, but flow_lookup (not protected) should use *max* of
struct mask_array.

Functions protected by ovs_lock:
* tbl_mask_array_del_mask
* tbl_mask_array_add_mask
* flow_mask_find
* ovs_flow_tbl_lookup_exact
* ovs_flow_tbl_num_masks

Signed-off-by: Tonghao Zhang <redacted>
---
 net/openvswitch/flow_table.c | 101 +++++++++++++++++++++----------------------
 1 file changed, 49 insertions(+), 52 deletions(-)

diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
index e59fac5..5257e4a 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c

@@ -546,7 +546,7 @@ static struct sw_flow *flow_lookup(struct flow_table *tbl,

                mask = rcu_dereference_ovsl(ma->masks[i]);
                if (!mask)
-                       continue;
+                       break;

                flow = masked_flow_lookup(ti, key, mask, n_mask_hit);
                if (flow) { /* Found */

@@ -640,15 +640,13 @@ struct sw_flow *ovs_flow_tbl_lookup_exact(struct flow_table *tbl,
        int i;

        /* Always called under ovs-mutex. */
-       for (i = 0; i < ma->max; i++) {
+       for (i = 0; i < ma->count; i++) {
                struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
                u32 __always_unused n_mask_hit;
                struct sw_flow_mask *mask;
                struct sw_flow *flow;

                mask = ovsl_dereference(ma->masks[i]);
-               if (!mask)
-                       continue;

                flow = masked_flow_lookup(ti, match->key, mask, &n_mask_hit);
                if (flow && ovs_identifier_is_key(&flow->id) &&

@@ -712,21 +710,31 @@ static struct table_instance *table_instance_expand(struct table_instance *ti,
        return table_instance_rehash(ti, ti->n_buckets * 2, ufid);
 }

-static void tbl_mask_array_delete_mask(struct mask_array *ma,
-                                      struct sw_flow_mask *mask)
+static void tbl_mask_array_del_mask(struct flow_table *tbl,
+                                   struct sw_flow_mask *mask)
 {
+       struct mask_array *ma = ovsl_dereference(tbl->mask_array);
        int i;

        /* Remove the deleted mask pointers from the array */
-       for (i = 0; i < ma->max; i++) {
-               if (mask == ovsl_dereference(ma->masks[i])) {
-                       RCU_INIT_POINTER(ma->masks[i], NULL);
-                       ma->count--;
-                       kfree_rcu(mask, rcu);
-                       return;
-               }
+       for (i = 0; i < ma->count; i++) {
+               if (mask == ovsl_dereference(ma->masks[i]))
+                       goto found;
        }
+
        BUG();
+       return;
+
+found:
+       rcu_assign_pointer(ma->masks[i], ma->masks[ma->count -1]);
+       RCU_INIT_POINTER(ma->masks[ma->count -1], NULL);
+       ma->count--;
+       kfree_rcu(mask, rcu);
+
+       /* Shrink the mask array if necessary. */
+       if (ma->max >= (MASK_ARRAY_SIZE_MIN * 2) &&
+           ma->count <= (ma->max / 3))
+               tbl_mask_array_realloc(tbl, ma->max / 2);
 }

 /* Remove 'mask' from the mask list, if it is not needed any more. */

@@ -740,17 +748,8 @@ static void flow_mask_remove(struct flow_table *tbl, struct sw_flow_mask *mask)
                BUG_ON(!mask->ref_count);
                mask->ref_count--;

-               if (!mask->ref_count) {
-                       struct mask_array *ma;
-
-                       ma = ovsl_dereference(tbl->mask_array);
-                       tbl_mask_array_delete_mask(ma, mask);
-
-                       /* Shrink the mask array if necessary. */
-                       if (ma->max >= (MASK_ARRAY_SIZE_MIN * 2) &&
-                           ma->count <= (ma->max / 3))
-                               tbl_mask_array_realloc(tbl, ma->max / 2);
-               }
+               if (!mask->ref_count)
+                       tbl_mask_array_del_mask(tbl, mask);
        }
 }

@@ -803,17 +802,38 @@ static struct sw_flow_mask *flow_mask_find(const struct flow_table *tbl,
        int i;

        ma = ovsl_dereference(tbl->mask_array);
-       for (i = 0; i < ma->max; i++) {
+       for (i = 0; i < ma->count; i++) {
                struct sw_flow_mask *t;
                t = ovsl_dereference(ma->masks[i]);

-               if (t && mask_equal(mask, t))
+               if (mask_equal(mask, t))
                        return t;
        }

        return NULL;
 }

+static int tbl_mask_array_add_mask(struct flow_table *tbl,
+                                  struct sw_flow_mask *new)
+{
+       struct mask_array *ma = ovsl_dereference(tbl->mask_array);
+       int err;
+
+       if (ma->count >= ma->max) {
+               err = tbl_mask_array_realloc(tbl, ma->max +
+                                             MASK_ARRAY_SIZE_MIN);
+               if (err)
+                       return err;
+       }
+
+       BUG_ON(ovsl_dereference(ma->masks[ma->count]));
+
+       rcu_assign_pointer(ma->masks[ma->count], new);
+       ma->count++;

There is no barrier for ma->count. Fastpath is accessing ma->count
without synchronization. Same issue with mask delete operation.

barrier will be added in v2,
In the fastpath, we use the ma->count and check ma->masks[*index] is
valid. if NULL we will break. so we can access ma->count without
synchronization in the fastpath.