netdev - Re: [Intel-wired-lan] [net-next PATCH v3 1/3] e1000: track BQL bytes regardless of skb or not

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Message-ID: <CAKgT0UdShvcviYP=VVp8c0OOESDnqsppArVeUhjxfM6XqX6HwQ@mail.gmail.com>
Date:   Mon, 12 Sep 2016 20:00:02 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        David Miller <davem@...emloft.net>,
        Cong Wang <xiyou.wangcong@...il.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        u9012063@...il.com, Netdev <netdev@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [net-next PATCH v3 1/3] e1000: track BQL bytes
 regardless of skb or not

On Mon, Sep 12, 2016 at 3:13 PM, John Fastabend
<john.fastabend@...il.com> wrote:
> The BQL API does not reference the sk_buff nor does the driver need to
> reference the sk_buff to calculate the length of a transmitted frame.
> This patch removes an sk_buff reference from the xmit irq path and
> also allows packets sent from XDP to use BQL.
>
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
>  drivers/net/ethernet/intel/e1000/e1000_main.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/e1000/e1000_main.c b/drivers/net/ethernet/intel/e1000/e1000_main.c
> index f42129d..62a7f8d 100644
> --- a/drivers/net/ethernet/intel/e1000/e1000_main.c
> +++ b/drivers/net/ethernet/intel/e1000/e1000_main.c
> @@ -3882,11 +3882,8 @@ static bool e1000_clean_tx_irq(struct e1000_adapter *adapter,
>                         if (cleaned) {
>                                 total_tx_packets += buffer_info->segs;
>                                 total_tx_bytes += buffer_info->bytecount;
> -                               if (buffer_info->skb) {
> -                                       bytes_compl += buffer_info->skb->len;
> -                                       pkts_compl++;
> -                               }
> -
> +                               bytes_compl += buffer_info->length;
> +                               pkts_compl++;
>                         }
>                         e1000_unmap_and_free_tx_resource(adapter, buffer_info);
>                         tx_desc->upper.data = 0;

Actually it might be worth looking into why we have two different
stats for tracking bytecount and segs.  From what I can tell the
pkts_compl value is never actually used.  The function doesn't even
use the value so it is just wasted cycles.  And as far as the bytes go
the accounting would be more accurate if you were to use bytecount
instead of buffer_info->skb->len.  You would just need to update the
xmit function to use that on the other side so that they match.

- Alex