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Date: Fri, 17 Jan 2020 19:09:51 +0300
From: Alexander Lobakin <alobakin@...nk.ru>
To: Maxim Mikityanskiy <maximmi@...lanox.com>
Cc: Edward Cree <ecree@...arflare.com>, netdev@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>,
Tariq Toukan <tariqt@...lanox.com>,
Jiri Pirko <jiri@...lanox.com>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] net: Fix packet reordering caused by GRO and
listified RX cooperation
Hi Maxim!
Maxim Mikityanskiy wrote 17.01.2020 18:09:
> Commit 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
> napi_gro_receive()") introduces batching of GRO_NORMAL packets in
> napi_skb_finish. However, dev_gro_receive, that is called just before
> napi_skb_finish, can also pass skbs to the networking stack: e.g., when
> the GRO session is flushed, napi_gro_complete is called, which passes
> pp
> directly to netif_receive_skb_internal, skipping napi->rx_list. It
> means
> that the packet stored in pp will be handled by the stack earlier than
> the packets that arrived before, but are still waiting in
> napi->rx_list.
> It leads to TCP reorderings that can be observed in the TCPOFOQueue
> counter in netstat.
>
> This commit fixes the reordering issue by making napi_gro_complete also
> use napi->rx_list, so that all packets going through GRO will keep
> their
> order.
>
> Fixes: 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
> napi_gro_receive()")
I don't think this is correct commit hash to place in "Fixes".
napi->rx_list was firstly introduced back in 323ebb61e32b
("net: use listified RX for handling GRO_NORMAL skbs"), but only
for napi_gro_frags() users. The one that you mentioned just made
use of listified Rx in napi_gro_receive() too. So I'd better tag
the first one, as this fix affects both receiving functions.
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> Cc: Alexander Lobakin <alobakin@...nk.ru>
> Cc: Edward Cree <ecree@...arflare.com>
> ---
> Alexander and Edward, please verify the correctness of this patch. If
> it's necessary to pass that SKB to the networking stack right away, I
> can change this patch to flush napi->rx_list by calling gro_normal_list
> first, instead of putting the SKB in the list.
I've just tested it on my usual 4-core MIPS board and got pretty
impressive results (VLAN NAT, iperf3, gro_normal_batch == 16):
thoughtput increase up to 40 Mbps (~840 -> ~880) and a huge reduce
of TCP retransmissions (about 80% of them I think).
So, from my point of view, the patch is completely correct and
very important. Thank you for this one!
Tested-by: Alexander Lobakin <alobakin@...nk.ru>
and, if applicable,
Reviewed-by: Alexander Lobakin <alobakin@...nk.ru>
> net/core/dev.c | 55 +++++++++++++++++++++++++-------------------------
> 1 file changed, 28 insertions(+), 27 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0ad39c87b7fd..db7a105bbc77 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5491,9 +5491,29 @@ static void flush_all_backlogs(void)
> put_online_cpus();
> }
>
> +/* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
> +static void gro_normal_list(struct napi_struct *napi)
> +{
> + if (!napi->rx_count)
> + return;
> + netif_receive_skb_list_internal(&napi->rx_list);
> + INIT_LIST_HEAD(&napi->rx_list);
> + napi->rx_count = 0;
> +}
> +
> +/* Queue one GRO_NORMAL SKB up for list processing. If batch size
> exceeded,
> + * pass the whole batch up to the stack.
> + */
> +static void gro_normal_one(struct napi_struct *napi, struct sk_buff
> *skb)
> +{
> + list_add_tail(&skb->list, &napi->rx_list);
> + if (++napi->rx_count >= gro_normal_batch)
> + gro_normal_list(napi);
> +}
> +
> INDIRECT_CALLABLE_DECLARE(int inet_gro_complete(struct sk_buff *,
> int));
> INDIRECT_CALLABLE_DECLARE(int ipv6_gro_complete(struct sk_buff *,
> int));
> -static int napi_gro_complete(struct sk_buff *skb)
> +static int napi_gro_complete(struct napi_struct *napi, struct sk_buff
> *skb)
> {
> struct packet_offload *ptype;
> __be16 type = skb->protocol;
> @@ -5526,7 +5546,8 @@ static int napi_gro_complete(struct sk_buff *skb)
> }
>
> out:
> - return netif_receive_skb_internal(skb);
> + gro_normal_one(napi, skb);
> + return NET_RX_SUCCESS;
> }
>
> static void __napi_gro_flush_chain(struct napi_struct *napi, u32
> index,
> @@ -5539,7 +5560,7 @@ static void __napi_gro_flush_chain(struct
> napi_struct *napi, u32 index,
> if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
> return;
> skb_list_del_init(skb);
> - napi_gro_complete(skb);
> + napi_gro_complete(napi, skb);
> napi->gro_hash[index].count--;
> }
>
> @@ -5641,7 +5662,7 @@ static void gro_pull_from_frag0(struct sk_buff
> *skb, int grow)
> }
> }
>
> -static void gro_flush_oldest(struct list_head *head)
> +static void gro_flush_oldest(struct napi_struct *napi, struct
> list_head *head)
> {
> struct sk_buff *oldest;
>
> @@ -5657,7 +5678,7 @@ static void gro_flush_oldest(struct list_head
> *head)
> * SKB to the chain.
> */
> skb_list_del_init(oldest);
> - napi_gro_complete(oldest);
> + napi_gro_complete(napi, oldest);
> }
>
> INDIRECT_CALLABLE_DECLARE(struct sk_buff *inet_gro_receive(struct
> list_head *,
> @@ -5733,7 +5754,7 @@ static enum gro_result dev_gro_receive(struct
> napi_struct *napi, struct sk_buff
>
> if (pp) {
> skb_list_del_init(pp);
> - napi_gro_complete(pp);
> + napi_gro_complete(napi, pp);
> napi->gro_hash[hash].count--;
> }
>
> @@ -5744,7 +5765,7 @@ static enum gro_result dev_gro_receive(struct
> napi_struct *napi, struct sk_buff
> goto normal;
>
> if (unlikely(napi->gro_hash[hash].count >= MAX_GRO_SKBS)) {
> - gro_flush_oldest(gro_head);
> + gro_flush_oldest(napi, gro_head);
> } else {
> napi->gro_hash[hash].count++;
> }
> @@ -5802,26 +5823,6 @@ struct packet_offload
> *gro_find_complete_by_type(__be16 type)
> }
> EXPORT_SYMBOL(gro_find_complete_by_type);
>
> -/* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
> -static void gro_normal_list(struct napi_struct *napi)
> -{
> - if (!napi->rx_count)
> - return;
> - netif_receive_skb_list_internal(&napi->rx_list);
> - INIT_LIST_HEAD(&napi->rx_list);
> - napi->rx_count = 0;
> -}
> -
> -/* Queue one GRO_NORMAL SKB up for list processing. If batch size
> exceeded,
> - * pass the whole batch up to the stack.
> - */
> -static void gro_normal_one(struct napi_struct *napi, struct sk_buff
> *skb)
> -{
> - list_add_tail(&skb->list, &napi->rx_list);
> - if (++napi->rx_count >= gro_normal_batch)
> - gro_normal_list(napi);
> -}
> -
> static void napi_skb_free_stolen_head(struct sk_buff *skb)
> {
> skb_dst_drop(skb);
Regards,
ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ
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