netdev - Re: [PATCH RFC net-next] sfc: add support for skb->xmit

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Date:	Thu, 16 Oct 2014 17:36:24 +0100
From:	Robert Stonehouse <rstonehouse@...arflare.com>
To:	Edward Cree <ecree@...arflare.com>,
	Daniel Borkmann <dborkman@...hat.com>
CC:	<davem@...emloft.net>, <nikolay@...hat.com>,
	<netdev@...r.kernel.org>, Shradha Shah <sshah@...arflare.com>,
	Jon Cooper <jcooper@...arflare.com>,
	linux-net-drivers <linux-net-drivers@...arflare.com>
Subject: Re: [PATCH RFC net-next] sfc: add support for skb->xmit_more

On 14/10/14 19:41, Edward Cree wrote:
> Don't ring the doorbell, and don't do PIO.  This will also prevent
>   TX Push, because there will be more than one buffer waiting when
>   the doorbell is rung.
>
> Signed-off-by: Edward Cree <ecree@...arflare.com>
> ---
>
> @@ -351,8 +343,6 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
>   	unsigned short dma_flags;
>   	int i = 0;
>   
> -	EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);
> -
>   	if (skb_shinfo(skb)->gso_size)
>   		return efx_enqueue_skb_tso(tx_queue, skb);

Would it be possible to keep a weaker version of this check i.e.
EFX_BUG_ON_PARANOID(tx_queue->write_count > tx_queue->insert_count);

> @@ -1258,14 +1249,13 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
>   			       struct sk_buff *skb)
>   {
>   	struct efx_nic *efx = tx_queue->efx;
> +	unsigned int old_insert_count = tx_queue->insert_count;
>   	int frag_i, rc;
>   	struct tso_state state;
>   
>   	/* Find the packet protocol and sanity-check it */
>   	state.protocol = efx_tso_check_protocol(skb);
>   
> -	EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);
> -
>   	rc = tso_start(&state, efx, skb);
>   	if (rc)
>   		goto mem_err;

The same would apply here.

Thanks
Rob

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