netdev - Re: [PATCH net-next v1 1/2] net: core: count drops from GRO

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Message-ID: <1e4ee1cf-c2b7-8ba3-7cb1-5c5cb3ff1e84@pensando.io>
Date:   Thu, 7 Jan 2021 16:50:10 -0800
From:   Shannon Nelson <snelson@...sando.io>
To:     Jesse Brandeburg <jesse.brandeburg@...el.com>,
        netdev@...r.kernel.org
Cc:     intel-wired-lan@...ts.osuosl.org,
        Eric Dumazet <edumazet@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net-next v1 1/2] net: core: count drops from GRO

On 1/6/21 1:55 PM, Jesse Brandeburg wrote:
> When drivers call the various receive upcalls to receive an skb
> to the stack, sometimes that stack can drop the packet. The good
> news is that the return code is given to all the drivers of
> NET_RX_DROP or GRO_DROP. The bad news is that no drivers except
> the one "ice" driver that I changed, check the stat and increment

If the stack is dropping the packet, isn't it up to the stack to track 
that, perhaps with something that shows up in netstat -s?  We don't 
really want to make the driver responsible for any drops that happen 
above its head, do we?

sln

> the dropped count. This is currently leading to packets that
> arrive at the edge interface and are fully handled by the driver
> and then mysteriously disappear.
>
> Rather than fix all drivers to increment the drop stat when
> handling the return code, emulate the already existing statistic
> update for NET_RX_DROP events for the two GRO_DROP locations, and
> increment the dev->rx_dropped associated with the skb.
>
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> ---
>   net/core/dev.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 8fa739259041..ef34043a9550 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6071,6 +6071,7 @@ static gro_result_t napi_skb_finish(struct napi_struct *napi,
>   		break;
>   
>   	case GRO_DROP:
> +		atomic_long_inc(&skb->dev->rx_dropped);
>   		kfree_skb(skb);
>   		break;
>   
> @@ -6159,6 +6160,7 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi,
>   		break;
>   
>   	case GRO_DROP:
> +		atomic_long_inc(&skb->dev->rx_dropped);
>   		napi_reuse_skb(napi, skb);
>   		break;
>