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From: "Michael Chan" <mchan@broadcom.com>
Subject: Re: [RFC] New driver API to speed up small packets xmits
Date: Tue, 15 May 2007 14:48:39 -0700
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Cc: "David Miller" <davem@davemloft.net>, ak@suse.de,
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To: "Roland Dreier" <rdreier@cisco.com>
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On Tue, 2007-05-15 at 13:52 -0700, Roland Dreier wrote:

> Well, IPoIB doesn't do netif_wake_queue() until half the device's TX
> queue is free, so we should get batching.  However, I'm not sure that
> I can count on a fudge factor ensuring that there's enough space to
> handle everything skb_gso_segment() gives me -- is there any reliable
> way to get an upper bound on how many segments a given gso skb will
> use when it's segmented?

Take a look at tg3.c.  I use (gso_segs * 3) as the upper bound.