netdev - Re: [PATCH net-next 2/3] net: qualcomm: rmnet: add tx packets aggregation

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Date:   Fri, 11 Nov 2022 09:11:41 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Subash Abhinov Kasiviswanathan (KS)" <quic_subashab@...cinc.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Daniele Palmas <dnlplm@...il.com>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "Sean Tranchetti" <quic_stranche@...cinc.com>,
        Jonathan Corbet <corbet@....net>,
        Bjørn Mork <bjorn@...k.no>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 2/3] net: qualcomm: rmnet: add tx packets
 aggregation

On Thu, 10 Nov 2022 18:17:09 -0700 Subash Abhinov Kasiviswanathan (KS)
wrote:
> The difference here is that hardware would use a single descriptor for 
> aggregation vs multiple descriptors for scatter gather.
> 
> I wonder if this issue is related to pacing though.
> Daniele, perhaps you can try this hack without enabling EGRESS 
> AGGREGATION and check if you are able to reach the same level of 
> performance for your scenario.
> 
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
> @@ -236,7 +236,7 @@ void rmnet_egress_handler(struct sk_buff *skb)
>          struct rmnet_priv *priv;
>          u8 mux_id;
> 
> -       sk_pacing_shift_update(skb->sk, 8);
> +       skb_orphan(skb);
> 
>          orig_dev = skb->dev;
>          priv = netdev_priv(orig_dev);

The pacing shift update is much cleaner than orphaning packets, IMHO.
And the aggregation should hold onto the original skbs (a list?) and
free them once the aggregate was transmitted.