gro: avoid checking for a failed search
Subsystems (2)
PATCH 1/1 gro: avoid checking for a failed search
After searching for a protocol handler in dev_gro_receive, checking for failure is redundant. Skip the failure code after finding the corresponding handler.
--- net/core/gro.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
net/core/gro.c +4 -4
@@ -522,13 +522,13 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff pp =INDIRECT_CALL_INET (ptype->callbacks.gro_receive, ipv6_gro_receive, inet_gro_receive, &gro_list->list, skb); -break ; +rcu_read_unlock (); + goto found; }rcu_read_unlock (); + goto normal; -if (&ptype->list == head) - goto normal; - +found:if (PTR_ERR (pp) == -EINPROGRESS ) { ret =GRO_CONSUMED ; goto ok;
Signature · 1 line
2.20.1
Jakub Kicinski
maintainerQuoted 3 lines · On Mon, 24 Oct 2022 07:17:49 +0200 Richard Gobert wrote:
After searching for a protocol handler in
dev_gro_receive, checking for failure is redundant. Skip the failure code after finding the corresponding handler.
Why does it matter? You see a measurable perf win?
Please fix the data on your system when you repost.
Quoted 1 line
Why does it matter? You see a measurable perf win?
In the common case, we will exit the loop with a break, so this patch eliminates an unnecessary check.
On some architectures this optimization might be done automatically by the compiler, but I think it will be better to make it explicit here. Although on x86 this optimization happens automatically, I noticed that on my build target (ARM/GCC) this does change the binary.
Quoted 11 lines · Richard Gobert
Quoted 2 lines
Why does it matter? You see a measurable perf win?
In the common case, we will exit the loop with a break, so this patch eliminates an unnecessary check.
On some architectures this optimization might be done automatically by the compiler, but I think it will be better to make it explicit here. Although on x86 this optimization happens automatically, I noticed that on my build target (ARM/GCC) this does change the binary.
What about taking this as an opportunity to reduce the indentation level by one tab ?
Untested patch:
net/core/gro.c +0 -0
100644
net/core/gro.c +0 -0
@@ -491,43 +491,44 @@ static enum gro_result dev_gro_receive(struct
napi_struct *napi, struct sk_buff
list_for_each_entry_rcu(ptype, head, list) {
if (ptype->type != type || !ptype->callbacks.gro_receive)
continue;
+ goto found_ptype;
+ }
+ rcu_read_unlock();
+ goto normal;- skb_set_network_header(skb, skb_gro_offset(skb)); - skb_reset_mac_len(skb); - BUILD_BUG_ON(sizeof_field(struct napi_gro_cb, zeroed)
!= sizeof(u32));
- BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed),
- sizeof(u32))); /* Avoid slow
unaligned acc */
- *(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0;
- NAPI_GRO_CB(skb)->flush = skb_has_frag_list(skb);
- NAPI_GRO_CB(skb)->is_atomic = 1;
- NAPI_GRO_CB(skb)->count = 1;
- if (unlikely(skb_is_gso(skb))) {
- NAPI_GRO_CB(skb)->count = skb_shinfo(skb)->gso_segs;
- /* Only support TCP at the moment. */
- if (!skb_is_gso_tcp(skb))
- NAPI_GRO_CB(skb)->flush = 1;
- }
-
- /* Setup for GRO checksum validation */
- switch (skb->ip_summed) {
- case CHECKSUM_COMPLETE:
- NAPI_GRO_CB(skb)->csum = skb->csum;
- NAPI_GRO_CB(skb)->csum_valid = 1;
- break;- case CHECKSUM_UNNECESSARY:
- NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1;
- break;
- }
+found_ptype:
+ skb_set_network_header(skb, skb_gro_offset(skb));
+ skb_reset_mac_len(skb);
+ BUILD_BUG_ON(sizeof_field(struct napi_gro_cb, zeroed) != sizeof(u32));
+ BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct napi_gro_cb, zeroed),
+ sizeof(u32))); /* Avoid slow unaligned acc */
+ *(u32 *)&NAPI_GRO_CB(skb)->zeroed = 0;
+ NAPI_GRO_CB(skb)->flush = skb_has_frag_list(skb);
+ NAPI_GRO_CB(skb)->is_atomic = 1;
+ NAPI_GRO_CB(skb)->count = 1;
+ if (unlikely(skb_is_gso(skb))) {
+ NAPI_GRO_CB(skb)->count = skb_shinfo(skb)->gso_segs;
+ /* Only support TCP at the moment. */
+ if (!skb_is_gso_tcp(skb))+ NAPI_GRO_CB(skb)->flush = 1;
+ }
- pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive,
- ipv6_gro_receive, inet_gro_receive,
- &gro_list->list, skb);
+ /* Setup for GRO checksum validation */
+ switch (skb->ip_summed) {
+ case CHECKSUM_COMPLETE:
+ NAPI_GRO_CB(skb)->csum = skb->csum;
+ NAPI_GRO_CB(skb)->csum_valid = 1;
+ break;
+ case CHECKSUM_UNNECESSARY:
+ NAPI_GRO_CB(skb)->csum_cnt = skb->csum_level + 1;
break;
}- rcu_read_unlock();
- if (&ptype->list == head)
- goto normal;
+ pp = INDIRECT_CALL_INET(ptype->callbacks.gro_receive,
+ ipv6_gro_receive, inet_gro_receive,
+ &gro_list->list, skb);
+
+ rcu_read_unlock();
if (PTR_ERR(pp) == -EINPROGRESS) {
ret = GRO_CONSUMED;Quoted 29 lines · Eric Dumazet
Quoted 11 lines · Richard Gobert
Quoted 2 lines
Why does it matter? You see a measurable perf win?
In the common case, we will exit the loop with a break, so this patch eliminates an unnecessary check.
On some architectures this optimization might be done automatically by the compiler, but I think it will be better to make it explicit here. Although on x86 this optimization happens automatically, I noticed that on my build target (ARM/GCC) this does change the binary.
What about taking this as an opportunity to reduce the indentation level by one tab ?
Untested patch:
net/core/gro.c +0
-0100644
net/core/gro.c +0
-0@@ -491,43 +491,44 @@ static enum gro_result dev_gro_receive(struct
napi_struct*napi, structsk_bufflist_for_each_entry_rcu(ptype, head, list) { if (ptype->type != type || !ptype->callbacks.gro_receive) continue;
net/core/gro.c
Quoted 4 lines
net/core/gro.c +4
-0+ goto found_ptype; + } +rcu_read_unlock (); + goto normal;
Or even better:
list_for_each_entry_rcu(ptype, head, list) {
if (ptype->type == type && ptype->callbacks.gro_receive)
goto found_ptype;
}
rcu_read_unlock();
goto normal;