netdev - Re: [PATCH 1/1] net: tcp: RTO restart

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Date:	Wed, 26 Feb 2014 11:52:49 -0800
From:	Nandita Dukkipati <nanditad@...gle.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	Per Hurtig <per.hurtig@....se>, Yuchung Cheng <ycheng@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Anna Brunström <anna.brunstrom@....se>,
	Andreas Petlund <apetlund@...ula.no>,
	Michael Welzl <michawe@....uio.no>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Subject: Re: [PATCH 1/1] net: tcp: RTO restart

On Wed, Feb 26, 2014 at 6:57 AM, Neal Cardwell <ncardwell@...gle.com> wrote:
> On Wed, Feb 26, 2014 at 4:50 AM, Per Hurtig <per.hurtig@....se> wrote:
>> Also, as your setup includes TLP we only have the RTO restart over TLP gain to start
>> with.
>
> My gut says the next thing to try is applying the "RTO restart" idea
> to the scheduling of the TLP probe (scheduling the TLP probe for
> write_queue_head_skb->when + tlp_timeout). Doing an RTO earlier can be
> a very bad thing, due to reseting the cwnd to 1. But doing a TLP
> earlier does not have much downside, and could have significant
> latency savings (though maybe Nandita already tried this at some
> point)...

+1 for applying RTO restart idea to scheduling a TLP. The thinking
with TLP at that time, was to send a probe approximately 1.5RTT after
the last "event" (which could be the transmit of a data packet or
receipt of an ACK). I did not try scheduling at
write_queue_head_skb->when + tlp_timeout, but I think it's worth an
experiment (may increase spurious TLPs by some amount which may be
OK).

Nandita
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