| Message ID | 20221024051744.GA48642@debian (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] gro: avoid checking for a failed search | expand |
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.
> 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.
On Wed, Nov 2, 2022 at 9:46 AM Richard Gobert <richardbgobert@gmail.com> wrote: > > > 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: diff --git a/net/core/gro.c b/net/core/gro.c index bc9451743307bc380cca96ae6995aa0a3b83d185..ddfe92c9a5e869d241931b72d6b3426a0e858468 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -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;
On Wed, Nov 2, 2022 at 11:20 AM Eric Dumazet <edumazet@google.com> wrote: > > On Wed, Nov 2, 2022 at 9:46 AM Richard Gobert <richardbgobert@gmail.com> wrote: > > > > > 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: > > diff --git a/net/core/gro.c b/net/core/gro.c > index bc9451743307bc380cca96ae6995aa0a3b83d185..ddfe92c9a5e869d241931b72d6b3426a0e858468 > 100644 > --- a/net/core/gro.c > +++ b/net/core/gro.c > @@ -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; 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;
diff --git a/net/core/gro.c b/net/core/gro.c index bc9451743307..a4e1b5a5be64 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -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;
After searching for a protocol handler in dev_gro_receive, checking for failure is redundant. Skip the failure code after finding the corresponding handler. Signed-off-by: Richard Gobert <richardbgobert@gmail.com> --- net/core/gro.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)