netdev - Re: [PATCH next] tcp: use zero-window when free

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Message-ID: <1387201280.19078.223.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 16 Dec 2013 05:41:20 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH next] tcp: use zero-window when free_space is low

On Mon, 2013-12-16 at 12:15 +0100, Florian Westphal wrote:
> Currently the kernel tries to announce a zero window when free_space
> is below the current receiver mss estimate.
> 
> When a sender is transmitting small packets, the receiver might be
> unable to shrink the receive window, because
> a) we cannot withdraw already-commited receive window, and,
> b) we have to round the current rwin up to a multiple of the wscale factor,
>    else we would shrink the current window.
> 
> This causes the receive buffer to fill up until the rmem limit is hit.
> When this happens, we start dropping packets.

I do not really understand the issue.
Do you have a packetdrill test to demonstrate it ?

Thanks !


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