On Fri, 14 Sep 2007 14:31:18 +0530 Krishna Kumar wrote:
> Add Documentation describing batching skb xmit capability.
>
> Signed-off-by: Krishna Kumar <[EMAIL PROTECTED]>
> ---
> batching_skb_xmit.txt | 107
> ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 107 insertions(+)
>
> diff -ruNp org/Documentation/networking/batching_skb_xmit.txt
> new/Documentation/networking/batching_skb_xmit.txt
> --- org/Documentation/networking/batching_skb_xmit.txt 1970-01-01
> 05:30:00.000000000 +0530
> +++ new/Documentation/networking/batching_skb_xmit.txt 2007-09-14
> 10:25:36.000000000 +0530
> @@ -0,0 +1,107 @@
> +
> +Section 4: Nitty gritty details for driver writers
> +--------------------------------------------------
> +
> + Batching is enabled from core networking stack only from softirq
> + context (NET_TX_SOFTIRQ), and dev_queue_xmit() doesn't use batching.
> +
> + This leads to the following situation:
> + A skb was not sent out as either driver lock was contested or
> + the device was blocked. When the softirq handler runs, it
> + moves all skbs from the device queue to the batch list, but
> + then it too could fail to send due to lock contention. The
> + next xmit (of a single skb) called from dev_queue_xmit() will
> + not use batching and try to xmit skb, while previous skbs are
> + still present in the batch list. This results in the receiver
> + getting out-of-order packets, and in case of TCP the sender
> + would have unnecessary retransmissions.
> +
> + To fix this problem, error cases where driver xmit gets called with a
> + skb must code as follows:
> + 1. If driver xmit cannot get tx lock, return NETDEV_TX_LOCKED
> + as usual. This allows qdisc to requeue the skb.
> + 2. If driver xmit got the lock but failed to send the skb, it
> + should return NETDEV_TX_BUSY but before that it should have
> + queue'd the skb to the batch list. In this case, the qdisc
queued
> + does not requeue the skb.
and then
Acked-by: Randy Dunlap <[EMAIL PROTECTED]>
Thanks,
---
~Randy
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