netdev - Re: [PATCH 1/4] e1000e: save skb counts in TX to avoid cache misses

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Date:	Mon, 26 Apr 2010 15:01:49 -0700
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] e1000e: save skb counts in TX to avoid cache misses

On Fri, Apr 23, 2010 at 17:25, Tom Herbert <therbert@...gle.com> wrote:
> In e1000_tx_map, precompute number of segements and bytecounts which
> are derived from fields in skb; these are stored in buffer_info.  When
> cleaning tx in e1000_clean_tx_irq use the values in the associated
> buffer_info for statistics counting, this eliminates cache misses
> on skb fields.
>
> Signed-off-by: Tom Herbert <therbert@...gle.com>
> ---
> diff --git a/drivers/net/e1000e/e1000.h b/drivers/net/e1000e/e1000.h
> index 12648a1..d6da75b 100644
> --- a/drivers/net/e1000e/e1000.h
> +++ b/drivers/net/e1000e/e1000.h
> @@ -188,6 +188,8 @@ struct e1000_buffer {
>                        unsigned long time_stamp;
>                        u16 length;
>                        u16 next_to_watch;
> +                       unsigned int segs;
> +                       unsigned int bytecount;
>                        u16 mapped_as_page;
>                };
>                /* Rx */
> diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
> index 5f70c43..4f5034a 100644
> --- a/drivers/net/e1000e/netdev.c
> +++ b/drivers/net/e1000e/netdev.c
> @@ -646,14 +635,8 @@ static bool e1000_clean_tx_irq(struct e1000_adapter *adapter)
>                        cleaned = (i == eop);
>
>                        if (cleaned) {
> -                               struct sk_buff *skb = buffer_info->skb;
> -                               unsigned int segs, bytecount;
> -                               segs = skb_shinfo(skb)->gso_segs ?: 1;
> -                               /* multiply data chunks by size of headers */
> -                               bytecount = ((segs - 1) * skb_headlen(skb)) +
> -                                           skb->len;
> -                               total_tx_packets += segs;
> -                               total_tx_bytes += bytecount;
> +                               total_tx_packets += buffer_info->segs;
> +                               total_tx_bytes += buffer_info->bytecount;
>                        }
>
>                        e1000_put_txbuf(adapter, buffer_info);
> @@ -3906,7 +3889,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
>        struct e1000_buffer *buffer_info;
>        unsigned int len = skb_headlen(skb);
>        unsigned int offset = 0, size, count = 0, i;
> -       unsigned int f;
> +       unsigned int f, bytecount, segs;
>
>        i = tx_ring->next_to_use;
>
> @@ -3965,7 +3948,13 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
>                }
>        }
>
> +       segs = skb_shinfo(skb)->gso_segs ?: 1;
> +       /* multiply data chunks by size of headers */
> +       bytecount = ((segs - 1) * skb_headlen(skb)) + skb->len;
> +
>        tx_ring->buffer_info[i].skb = skb;
> +       tx_ring->buffer_info[i].segs = segs;
> +       tx_ring->buffer_info[i].bytecount = bytecount;
>        tx_ring->buffer_info[first].next_to_watch = i;
>
>        return count;
> --
>

I have added your patches to my queue of e1000e patches, thanks.

-- 
Cheers,
Jeff