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Date: Fri, 30 Sep 2022 13:19:18 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Paolo Abeni <pabeni@...hat.com> Cc: Eric Dumazet <eric.dumazet@...il.com>, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, netdev <netdev@...r.kernel.org>, Coco Li <lixiaoyan@...gle.com> Subject: Re: [PATCH net-next] gro: add support of (hw)gro packets to gro stack On Fri, Sep 30, 2022 at 1:00 PM Eric Dumazet <edumazet@...gle.com> wrote: > > On Fri, Sep 30, 2022 at 12:53 PM Eric Dumazet <edumazet@...gle.com> wrote: > > > > On Fri, Sep 30, 2022 at 1:45 AM Paolo Abeni <pabeni@...hat.com> wrote: > > > > > > On Thu, 2022-09-29 at 18:44 -0700, Eric Dumazet wrote: > > > > From: Coco Li <lixiaoyan@...gle.com> > > > > > > > > Current GRO stack only supports incoming packets containing > > > > one frame/MSS. > > > > > > > > This patch changes GRO to accept packets that are already GRO. > > > > > > > > HW-GRO (aka RSC for some vendors) is very often limited in presence > > > > of interleaved packets. Linux SW GRO stack can complete the job > > > > and provide larger GRO packets, thus reducing rate of ACK packets > > > > and cpu overhead. > > > > > > > > This also means BIG TCP can be used, even if HW-GRO/RSC was > > > > able to cook ~64 KB GRO packets. > > > > > > > > Co-Developed-by: Eric Dumazet <edumazet@...gle.com> > > > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > > > > Signed-off-by: Coco Li <lixiaoyan@...gle.com> > > > > --- > > > > net/core/gro.c | 13 +++++++++---- > > > > net/ipv4/tcp_offload.c | 7 ++++++- > > > > 2 files changed, 15 insertions(+), 5 deletions(-) > > > > > > > > diff --git a/net/core/gro.c b/net/core/gro.c > > > > index b4190eb084672fb4f2be8b437eccb4e8507ff63f..d8e159c4bdf553508cd123bee4f5251908ede9fe 100644 > > > > --- a/net/core/gro.c > > > > +++ b/net/core/gro.c > > > > @@ -160,6 +160,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) > > > > unsigned int gro_max_size; > > > > unsigned int new_truesize; > > > > struct sk_buff *lp; > > > > + int segs; > > > > > > > > /* pairs with WRITE_ONCE() in netif_set_gro_max_size() */ > > > > gro_max_size = READ_ONCE(p->dev->gro_max_size); > > > > @@ -175,6 +176,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) > > > > return -E2BIG; > > > > } > > > > > > > > + segs = NAPI_GRO_CB(skb)->count; > > > > lp = NAPI_GRO_CB(p)->last; > > > > pinfo = skb_shinfo(lp); > > > > > > > > @@ -265,7 +267,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) > > > > lp = p; > > > > > > > > done: > > > > - NAPI_GRO_CB(p)->count++; > > > > + NAPI_GRO_CB(p)->count += segs; > > > > p->data_len += len; > > > > p->truesize += delta_truesize; > > > > p->len += len; > > > > @@ -496,8 +498,10 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff > > > > 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_is_gso(skb) || skb_has_frag_list(skb); > > > > + NAPI_GRO_CB(skb)->flush = skb_has_frag_list(skb); > > > > NAPI_GRO_CB(skb)->is_atomic = 1; > > > > + NAPI_GRO_CB(skb)->count = max_t(u16, 1, > > > > + skb_shinfo(skb)->gso_segs); > > > > > > > > /* Setup for GRO checksum validation */ > > > > switch (skb->ip_summed) { > > > > @@ -545,10 +549,10 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff > > > > else > > > > gro_list->count++; > > > > > > > > - NAPI_GRO_CB(skb)->count = 1; > > > > NAPI_GRO_CB(skb)->age = jiffies; > > > > NAPI_GRO_CB(skb)->last = skb; > > > > - skb_shinfo(skb)->gso_size = skb_gro_len(skb); > > > > + if (!skb_is_gso(skb)) > > > > + skb_shinfo(skb)->gso_size = skb_gro_len(skb); > > > > list_add(&skb->list, &gro_list->list); > > > > ret = GRO_HELD; > > > > > > > > @@ -660,6 +664,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb) > > > > > > > > skb->encapsulation = 0; > > > > skb_shinfo(skb)->gso_type = 0; > > > > + skb_shinfo(skb)->gso_size = 0; > > > > if (unlikely(skb->slow_gro)) { > > > > skb_orphan(skb); > > > > skb_ext_reset(skb); > > > > diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c > > > > index a844a0d38482d916251f3aca4555c75c9770820c..0223bbfe9568064b47bc6227d342a4d25c9edfa7 100644 > > > > --- a/net/ipv4/tcp_offload.c > > > > +++ b/net/ipv4/tcp_offload.c > > > > @@ -255,7 +255,12 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb) > > > > > > > > mss = skb_shinfo(p)->gso_size; > > > > > > > > - flush |= (len - 1) >= mss; > > > > + if (skb_is_gso(skb)) { > > > > + flush |= (mss != skb_shinfo(skb)->gso_size); > > > > + flush |= ((skb_gro_len(p) % mss) != 0); > > > > > > If I read correctly, the '(skb_gro_len(p) % mss) != 0' codition can be > > > true only if 'p' was an HW GRO packet (or at least a gso packet before > > > entering the GRO engine), am I correct? In that case 'p' staged into > > > the GRO hash up to the next packet (skb), just to be flushed. > > > > > > Should the above condition be instead: > > > > > > flush |= ((skb_gro_len(skb) % mss) != 0); > > > > Yes, probable typo. > > > > > ? > > > > > > And possibly use that condition while initializing > > > NAPI_GRO_CB(skb)->flush in dev_gro_receive() ? > > > > Not sure, this would add an extra test in dev_gro_receive() > > > > It seems better to leave the test here, because the prior condition > > needs to stay here. > > > > if (skb_is_gso(skb)) { > > flush |= (mss != skb_shinfo(skb)->gso_size); > > > > Oh well, I think Coco missed the fact that the ((skb_gro_len(skb) % mss) != 0) > condition needs to be put after label out_check_final. > > For example, if MSS==1000, and p has 4 segments, we still want to > aggregate skb into p > if skb payload is not a multiple of MSS. > Relative diff would be: diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c index 0223bbfe9568064b47bc6227d342a4d25c9edfa7..79996b007bd64635aea27e3fddf291abe10ceca1 100644 --- a/net/ipv4/tcp_offload.c +++ b/net/ipv4/tcp_offload.c @@ -255,26 +255,27 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb) mss = skb_shinfo(p)->gso_size; - if (skb_is_gso(skb)) { + if (unlikely(skb_is_gso(skb))) flush |= (mss != skb_shinfo(skb)->gso_size); - flush |= ((skb_gro_len(p) % mss) != 0); - } else { + else flush |= (len - 1) >= mss; - } + flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq); #ifdef CONFIG_TLS_DEVICE flush |= p->decrypted ^ skb->decrypted; #endif if (flush || skb_gro_receive(p, skb)) { - mss = 1; - goto out_check_final; + flush = 0; + goto check_flags; } tcp_flag_word(th2) |= flags & (TCP_FLAG_FIN | TCP_FLAG_PSH); out_check_final: - flush = len < mss; + flush = len != NAPI_GRO_CB(skb)->count * mss; + +check_flags: flush |= (__force int)(flags & (TCP_FLAG_URG | TCP_FLAG_PSH | TCP_FLAG_RST | TCP_FLAG_SYN | TCP_FLAG_FIN));
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