netdev - Re: Bug in computing data_len in tcp

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Message-ID: <1322730937.2335.6.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Thu, 01 Dec 2011 10:15:37 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Linux Netdev List <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: Bug in computing data_len in tcp_sendmsg?

Le mercredi 30 novembre 2011 à 21:09 -0800, Tom Herbert a écrit :
> > Or the "bug" was to assume that skb was headless.
> > It was true until recently.
> >
> > We recently added commit f07d960df33c5aef
> > (tcp: avoid frag allocation for small frames)
> >
> > to avoid page allocation for small frames.
> >
> > So now, skb can contain in head part of tcp data.
> 
> Yes, reverting that patch seems to fix the problem.  Eric, do you have
> an idea what should be used to determine length of headers in an skb
> now (mac through transport).

I dont know why its even necessary :

TSO enabled NIC all provide hardware counters, so why even bother
computing tx_bytes ourself ?

skb->len is appropriate for BQL, as long as producers/consumer use the
same skb->len. 1 or 2% error is not a problem if not cumulative ?



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