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Date:	Mon, 5 May 2014 11:47:02 -0300
From:	Ezequiel Garcia <>
Cc:	"David S. Miller" <>,
	Eric Dumazet <>,,
	Thomas Petazzoni <>,
	Gregory Clement <>,
	Simon Guinot <>,
	Willy Tarreau <>, Tawfik Bayouk <>,
	Lior Amsalem <>,
	Simon Guinot <>
Subject: Re: [PATCH 3/3] net: mvneta: Introduce a software TSO implementation

Hi all,

On 10 Apr 07:58 PM, Ezequiel Garcia wrote:
> +
> +	/* Calculate expected number of TX descriptors */
> +	desc_count = skb_shinfo(skb)->gso_segs * 2 + skb_shinfo(skb)->nr_frags;
> +	if ((txq->count + desc_count) >= txq->size)
> +		return 0;
> +

Is this calculus correct? Does it give the accurate number of needed
descriptors or is it an approximation?

Tilera's tilegx driver does a much stricter descriptor count (see
tso_count_edescs). This functions loops through the skb_frag_t fragments
as it's done later in the data egress, hence strictly counting the
needed descriptors.

However, as it's a much heavier routine than the one shown above,
I'm wondering if we can get away without it.

Willy, Any ideas here?
Ezequiel GarcĂ­a, Free Electrons
Embedded Linux, Kernel and Android Engineering
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