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Date: Tue, 1 Oct 2019 19:06:55 -0700
From: Pravin Shelar <pshelar@....org>
To: Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc: Greg Rose <gvrose8192@...il.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 5/9] net: openvswitch: optimize flow-mask looking up
On Sun, Sep 29, 2019 at 7:09 PM <xiangxia.m.yue@...il.com> wrote:
>
> From: Tonghao Zhang <xiangxia.m.yue@...il.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.
>
> 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 <xiangxia.m.yue@...il.com>
> ---
> 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.
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