On Fri, Mar 12, 2021 at 5:22 PM Alexander Lobakin <aloba...@pm.me> wrote: > > GRO bucket index doesn't change through the entire function. > Store a pointer to the corresponding bucket on stack once and use > it later instead of dereferencing again and again. > > Signed-off-by: Alexander Lobakin <aloba...@pm.me> > --- > net/core/dev.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index adc42ba7ffd8..ee124aecb8a2 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -5957,6 +5957,7 @@ static void gro_flush_oldest(struct napi_struct *napi, > struct list_head *head) > static enum gro_result dev_gro_receive(struct napi_struct *napi, struct > sk_buff *skb) > { > u32 bucket = skb_get_hash_raw(skb) & (GRO_HASH_BUCKETS - 1); > + struct gro_list *gro_list = &napi->gro_hash[bucket]; > struct list_head *head = &offload_base; > struct packet_offload *ptype; > __be16 type = skb->protocol; > @@ -6024,7 +6025,7 @@ static enum gro_result dev_gro_receive(struct > napi_struct *napi, struct sk_buff > if (pp) { > skb_list_del_init(pp); > napi_gro_complete(napi, pp); > - napi->gro_hash[bucket].count--; > + gro_list->count--; > } > > if (same_flow) > @@ -6033,10 +6034,10 @@ static enum gro_result dev_gro_receive(struct > napi_struct *napi, struct sk_buff > if (NAPI_GRO_CB(skb)->flush) > goto normal; > > - if (unlikely(napi->gro_hash[bucket].count >= MAX_GRO_SKBS)) { > + if (unlikely(gro_list->count >= MAX_GRO_SKBS)) { > gro_flush_oldest(napi, gro_head); > } else { > - napi->gro_hash[bucket].count++; > + gro_list->count++; > } > NAPI_GRO_CB(skb)->count = 1; > NAPI_GRO_CB(skb)->age = jiffies; > @@ -6050,7 +6051,7 @@ static enum gro_result dev_gro_receive(struct > napi_struct *napi, struct sk_buff > if (grow > 0) > gro_pull_from_frag0(skb, grow); > ok: > - if (napi->gro_hash[bucket].count) { > + if (gro_list->count) { > if (!test_bit(bucket, &napi->gro_bitmask)) > __set_bit(bucket, &napi->gro_bitmask); > } else if (test_bit(bucket, &napi->gro_bitmask)) { > -- > 2.30.2 > >
This adds more register pressure, do you have precise measures to confirm this change is a win ? Presumably the compiler should be able to optimize the code just fine, it can see @bucket does not change.