On Thu, 2021-02-04 at 13:31 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <eduma...@google.com>
>
> Commit c80794323e82 ("net: Fix packet reordering caused by GRO and
> listified RX cooperation") had the unfortunate effect of adding
> latencies in common workloads.
>
> Before the patch, GRO packets were immediately passed to
> upper stacks.
>
> After the patch, we can accumulate quite a lot of GRO
> packets (depdending on NAPI budget).
>
Why napi budget ? looking at the code it seems to be more related to
MAX_GRO_SKBS * gro_normal_batch, since we are counting GRO SKBs as 1
but maybe i am missing some information about the actual issue you are
hitting.
> My fix is counting in napi->rx_count number of segments
> instead of number of logical packets.
>
> Fixes: c80794323e82 ("net: Fix packet reordering caused by GRO and
> listified RX cooperation")
> Signed-off-by: Eric Dumazet <eduma...@google.com>
> Bisected-by: John Sperbeck <jsperb...@google.com>
> Tested-by: Jian Yang <jiany...@google.com>
> Cc: Maxim Mikityanskiy <maxi...@mellanox.com>
> Cc: Alexander Lobakin <aloba...@dlink.ru>
> Cc: Saeed Mahameed <sae...@mellanox.com>
> Cc: Edward Cree <ec...@solarflare.com>
> ---
> net/core/dev.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index
> a979b86dbacda9dfe31dd8b269024f7f0f5a8ef1..449b45b843d40ece7dd1e2ed6a5
> 996ee1db9f591 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5735,10 +5735,11 @@ static void gro_normal_list(struct
> napi_struct *napi)
> /* 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)
> +static void gro_normal_one(struct napi_struct *napi, struct sk_buff
> *skb, int segs)
> {
> list_add_tail(&skb->list, &napi->rx_list);
> - if (++napi->rx_count >= gro_normal_batch)
> + napi->rx_count += segs;
> + if (napi->rx_count >= gro_normal_batch)
> gro_normal_list(napi);
> }
>
> @@ -5777,7 +5778,7 @@ static int napi_gro_complete(struct napi_struct
> *napi, struct sk_buff *skb)
> }
>
> out:
> - gro_normal_one(napi, skb);
> + gro_normal_one(napi, skb, NAPI_GRO_CB(skb)->count);
Seems correct to me,
Reviewed-by: Saeed Mahameed <sae...@nvidia.com>
