netdev - Re: [PATCH v2 1/2] tcp: add new tcp_mtu_probe

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Message-Id: <20190809.125901.428600986132688806.davem@davemloft.net>
Date:   Fri, 09 Aug 2019 12:59:01 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     johunt@...mai.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, ncardwell@...gle.com
Subject: Re: [PATCH v2 1/2] tcp: add new tcp_mtu_probe_floor sysctl

From: Josh Hunt <johunt@...mai.com>
Date: Wed,  7 Aug 2019 19:52:29 -0400

> The current implementation of TCP MTU probing can considerably
> underestimate the MTU on lossy connections allowing the MSS to get down to
> 48. We have found that in almost all of these cases on our networks these
> paths can handle much larger MTUs meaning the connections are being
> artificially limited. Even though TCP MTU probing can raise the MSS back up
> we have seen this not to be the case causing connections to be "stuck" with
> an MSS of 48 when heavy loss is present.
> 
> Prior to pushing out this change we could not keep TCP MTU probing enabled
> b/c of the above reasons. Now with a reasonble floor set we've had it
> enabled for the past 6 months.
> 
> The new sysctl will still default to TCP_MIN_SND_MSS (48), but gives
> administrators the ability to control the floor of MSS probing.
> 
> Signed-off-by: Josh Hunt <johunt@...mai.com>

Applied.