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From: "Anatoly Sivov" <mm05@mail.ru>
To: "Vijay Subramanian" <subramanian.vijay@gmail.com>
Cc: netdev@vger.kernel.org
Subject: Re: tcp_mtu_probe implementation details
Date: Wed, 21 Dec 2011 13:50:30 +0400	[thread overview]
Message-ID: <op.v6t2ygnyfzo5me@stalin> (raw)
In-Reply-To: <CAGK4HS93u=3muZu_rkqK7FSacTHUytK5H6_dMNo_uOQY738R_g@mail.gmail.com>

Hello Vijay,

Thank you for your response.

>> The other question is about size_needed variable.
>> It is assigned to value probe_size + (tp->reordering + 1) *  
>> tp->mss_cache
>> And that is not clear for me.
>> What is this "(tp->reordering + 1) * tp->mss_cache" addition?
>>
>
> I think the idea is that you want enough bytes in the write_queue so
> that even if the probe is lost, the sender will get an ack even if
> there is reordering in the network. Without sufficient bytes, the
> probe will not be sent. This is what I make of the code but I could be
> wrong.

I believe, I found the explanation of this addition in RFC 4821:
   "TCP Fast Retransmit is not robust unless there are
    sufficient segments following a probe; that is, the sender SHOULD
    have enough data queued and sufficient receiver window to send the
    probe plus at least Tcprexmtthresh [RFC2760] additional segments."

However, I'm still confused with magic number 11 in "tp->snd_cwnd < 11"  
check.

Thanks.

  reply	other threads:[~2011-12-21  9:50 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-20 21:49 tcp_mtu_probe implementation details Anatoly Sivov
2011-12-20 22:33 ` Vijay Subramanian
2011-12-21  9:50   ` Anatoly Sivov [this message]
2011-12-24 15:03     ` John Heffner
2011-12-24 16:15       ` Anatoly Sivov

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