netdev - Re: [PATCH net-next v2] tcp: avoid reducing cwnd when ACK+DSACK is received

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Message-ID: <1420734325.5947.61.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 08 Jan 2015 08:25:25 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	Sébastien Barré <sebastien.barre@...ouvain.be>,
	David Miller <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>,
	Gregory Detal <gregory.detal@...ouvain.be>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next v2] tcp: avoid reducing cwnd when ACK+DSACK is
 received

On Thu, 2015-01-08 at 10:49 -0500, Neal Cardwell wrote:
> On Thu, Jan 8, 2015 at 10:39 AM, Sébastien Barré
> <sebastien.barre@...ouvain.be> wrote:
> > What do you and Neal think ?
> 
> My preference is to have the whole expression detecting the case where
> the receiver got the probe packet encoded in a single expression. I
> don't have a strong feeling about whether it should be stored in a
> bool (to reduce the size of the diff) or written directly into the if
> () expression (to reduce the size of the code). I'll defer to Eric on
> which he thinks is better. :-)

There is no shame using helpers with nice names to help understand this
TCP stack. Even if the helper is used exactly once.

In this case, it seems we test 2 different conditions, so this could use
2 helpers with self describing names.

When I see : 

> +     if (((ack == tp->tlp_high_seq) &&
> +          !(flag & (FLAG_SND_UNA_ADVANCED |
> +                    FLAG_NOT_DUP | FLAG_DATA_SACKED))) ||
> +         (!before(ack, tp->tlp_high_seq) && (flag & FLAG_DSACKING_ACK))) {
>               tp->tlp_high_seq = 0;

My brain hurts.


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