Redefine clear_vlan to initialize one struct vlan_head
Define clear_vlans to initialize key.eth.vlan and key.eth.cvlan
Calls the revised functions accurately
Reasoning:
For vlan packet, current code calls clear_vlan unnecessarily,
since parse_vlan sets key->eth.vlan and key->eth.cvlan correctly.
Only special case where return value <=0 needs inialization
certail key.eth.vlan or key.eth.cvlan specifically.
For none-vlan case, parse_vlan returns on the first parse_vlan_tag
which returns 0, in this case, calls clear_vlan
For MAC_PROTO_NONE, logic is intact after this revision
Signed-off-by: Eddy Tao <[email protected]>
---
net/openvswitch/flow.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
index e20d1a973417..30a90597cab6 100644
--- a/net/openvswitch/flow.c
+++ b/net/openvswitch/flow.c
@@ -480,12 +480,16 @@ static int parse_vlan_tag(struct sk_buff *skb, struct vlan_head *key_vh,
return 1;
}
-static void clear_vlan(struct sw_flow_key *key)
+static inline void clear_vlan(struct vlan_head *vlan)
{
- key->eth.vlan.tci = 0;
- key->eth.vlan.tpid = 0;
- key->eth.cvlan.tci = 0;
- key->eth.cvlan.tpid = 0;
+ vlan->tci = 0;
+ vlan->tpid = 0;
+}
+
+static inline void clear_vlans(struct sw_flow_key *key)
+{
+ clear_vlan(&key->eth.vlan);
+ clear_vlan(&key->eth.cvlan);
}
static int parse_vlan(struct sk_buff *skb, struct sw_flow_key *key)
@@ -498,14 +502,18 @@ static int parse_vlan(struct sk_buff *skb, struct sw_flow_key *key)
} else {
/* Parse outer vlan tag in the non-accelerated case. */
res = parse_vlan_tag(skb, &key->eth.vlan, true);
- if (res <= 0)
+ if (res <= 0) {
+ clear_vlans(key);
return res;
+ }
}
/* Parse inner vlan tag. */
res = parse_vlan_tag(skb, &key->eth.cvlan, false);
- if (res <= 0)
+ if (res <= 0) {
+ clear_vlan(&key->eth.cvlan);
return res;
+ }
return 0;
}
@@ -918,8 +926,8 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
skb_reset_mac_header(skb);
/* Link layer. */
- clear_vlan(key);
if (ovs_key_mac_proto(key) == MAC_PROTO_NONE) {
+ clear_vlans(key);
if (unlikely(eth_type_vlan(skb->protocol)))
return -EINVAL;
--
2.27.0
On Tue, Feb 07, 2023 at 12:31:33PM +0800, Eddy Tao wrote:
> Redefine clear_vlan to initialize one struct vlan_head
> Define clear_vlans to initialize key.eth.vlan and key.eth.cvlan
> Calls the revised functions accurately
>
> Reasoning:
>
> For vlan packet, current code calls clear_vlan unnecessarily,
> since parse_vlan sets key->eth.vlan and key->eth.cvlan correctly.
> Only special case where return value <=0 needs inialization
> certail key.eth.vlan or key.eth.cvlan specifically.
>
> For none-vlan case, parse_vlan returns on the first parse_vlan_tag
> which returns 0, in this case, calls clear_vlan
>
> For MAC_PROTO_NONE, logic is intact after this revision
>
> Signed-off-by: Eddy Tao <[email protected]>
This seems like a complex, and perhaps error-prone, way to avoid
writing a few bytes. I do tend to think the extra code complexity
is not worth it without some performance justification.
OTOH, I think that perhaps a better question might be: do the bytes need to
be cleared under any circumstances? I suspect key is discarded when an
error occurs.
> ---
> net/openvswitch/flow.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> index e20d1a973417..30a90597cab6 100644
> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -480,12 +480,16 @@ static int parse_vlan_tag(struct sk_buff *skb, struct vlan_head *key_vh,
> return 1;
> }
>
> -static void clear_vlan(struct sw_flow_key *key)
> +static inline void clear_vlan(struct vlan_head *vlan)
> {
> - key->eth.vlan.tci = 0;
> - key->eth.vlan.tpid = 0;
> - key->eth.cvlan.tci = 0;
> - key->eth.cvlan.tpid = 0;
> + vlan->tci = 0;
> + vlan->tpid = 0;
> +}
> +
> +static inline void clear_vlans(struct sw_flow_key *key)
> +{
> + clear_vlan(&key->eth.vlan);
> + clear_vlan(&key->eth.cvlan);
> }
This is a nice cleanup, IMHO :)
>
> static int parse_vlan(struct sk_buff *skb, struct sw_flow_key *key)
> @@ -498,14 +502,18 @@ static int parse_vlan(struct sk_buff *skb, struct sw_flow_key *key)
> } else {
> /* Parse outer vlan tag in the non-accelerated case. */
> res = parse_vlan_tag(skb, &key->eth.vlan, true);
> - if (res <= 0)
> + if (res <= 0) {
> + clear_vlans(key);
I think this makes more sense in the caller.
> return res;
> + }
> }
>
> /* Parse inner vlan tag. */
> res = parse_vlan_tag(skb, &key->eth.cvlan, false);
> - if (res <= 0)
> + if (res <= 0) {
> + clear_vlan(&key->eth.cvlan);
> return res;
> + }
>
> return 0;
> }
> @@ -918,8 +926,8 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
> skb_reset_mac_header(skb);
>
> /* Link layer. */
> - clear_vlan(key);
> if (ovs_key_mac_proto(key) == MAC_PROTO_NONE) {
> + clear_vlans(key);
> if (unlikely(eth_type_vlan(skb->protocol)))
> return -EINVAL;
I think you missed the following case further down:
if (unlikely(key->eth.type == htons(0)))
return -ENOMEM;
Hi, Simon:
Thanks for looking into this. by looking into the compiled
instructions, i am convinced the patch is logically correct but not help
in performance, and it adds complexity,
Below function is actually optimized to one movq instruction with no
special -O settings on my centos8, which seems good enough for me
static void clear_vlan(struct sw_flow_key *key)
{
key->eth.vlan.tci = 0;
key->eth.vlan.tpid = 0;
key->eth.cvlan.tci = 0;
key->eth.cvlan.tpid = 0;
}
optimized to movq $0x0,0x158(%rbx)
I am withdrawing this patch
About your comment below, since it is after the parse_vlan handling, the
code looks fine and does not affect the logic of the patch
>>I think you missed the following case further down: >>>>if
(unlikely(key->eth.type == htons(0))) Have a great day
eddy