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Date: Tue, 8 Oct 2019 11:15:39 +0800
From: Tonghao Zhang <xiangxia.m.yue@...il.com>
To: Pravin Shelar <pshelar@....org>
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 Wed, Oct 2, 2019 at 10:03 AM Pravin Shelar <pshelar@....org> wrote:
>
> 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.
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.
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