netdev - Re: [RFC] New driver API to speed up small packets xmits

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Message-ID: <adatzuerr47.fsf@cisco.com>
Date:	Tue, 15 May 2007 09:25:28 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Andi Kleen <ak@...e.de>
Cc:	Krishna Kumar2 <krkumar2@...ibm.com>, netdev@...r.kernel.org
Subject: Re: [RFC] New driver API to speed up small packets xmits

 > > As I said before, getting multiple packets in one call to xmit would
 > > be nice for amortizing per-xmit overhead in IPoIB.  So it would be
 > > nice if the cases where the stack does GSO ended up passing all the
 > > segments into the driver in one go.
 > 
 > Well TCP does upto 64k -- that is what GSO is about.

I see... the plan would be to add NETIF_F_GSO_SOFTWARE to the device
features and use skb_gso_segment() in the netdevice driver?  (I just
studied GSO more carefully -- I hadn't realized that was possible)

I'll have to think about implementing that for IPoIB.  One issue I see
is if I have, say, 4 free entries in my send queue and skb_gso_segment()
gives me back 5 packets to send.  It's not clear I can recover at that
point -- I guess I have to check against gso_segs in the xmit routine
before actually doing the segmentation.

 - R.
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