netdev - Re: [PATCH net-next] tcp: RFC6298 supersedes RFC2988bis

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Date:	Sun, 15 Apr 2012 22:01:01 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jerry Chu <hkchu@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net-next] tcp: RFC6298 supersedes RFC2988bis

On Sun, 2012-04-15 at 11:33 -0700, Jerry Chu wrote:
> [send again - it looks like my previous comment was lost...]
> 
> On Thu, Apr 12, 2012 at 10:48 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Updates some comments to track RFC6298
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: H.K. Jerry Chu <hkchu@...gle.com>
> > Cc: Tom Herbert <therbert@...gle.com>
> > ---
> > BTW, one side effect of the TCP_TIMEOUT_INIT change (3 -> 1) is
> > () latency is 200% worse:
> 
> Or even worse - 300% (3/1)?

well, 3 instead of 1 is a 200% increase ;)

> 
> >
> > It fires every 200ms and scans 40% of hash table each time, listener
> > socket held.
> 
> If this becomes a real issue we could decrease TCP_SYNQ_INTERVAL,
> essentially making the keepalive timer fire more often, but each time with
> less work to do?

Hmm... 200ms is already aggressive for power saving

> 
> Also why is
> budget = 2 * (lopt->nr_table_entries / (timeout / interval));
> rather than
> budget = (lopt->nr_table_entries / (timeout / interval)) + 1;
> ?

Thats because if we do that, retransmits could be delayed by 100%,
instead of 50% with this solution.

(right now it takes 2.5 rounds to scan whole table, so a one sec 'timer'
can be fired after 1.6 second)



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