netdev - Re: [PATCH net] tcp: fix receive buffer autotuning to trigger for any valid advertised MSS

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Message-ID: <20201207105345.4a4474f3@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Mon, 7 Dec 2020 10:53:45 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>
Cc:     <netdev@...r.kernel.org>, <stable@...r.kernel.org>,
        <edumazet@...gle.com>, <ycheng@...gle.com>, <ncardwell@...gle.com>,
        <weiwan@...gle.com>, <astroh@...zon.com>, <benh@...zon.com>
Subject: Re: [PATCH net] tcp: fix receive buffer autotuning to trigger for
 any valid advertised MSS

On Mon, 7 Dec 2020 11:46:25 +0000 Hazem Mohamed Abuelfotoh wrote:
>     Previously receiver buffer auto-tuning starts after receiving
>     one advertised window amount of data.After the initial
>     receiver buffer was raised by
>     commit a337531b942b ("tcp: up initial rmem to 128KB
>     and SYN rwin to around 64KB"),the receiver buffer may
>     take too long for TCP autotuning to start raising
>     the receiver buffer size.
>     commit 041a14d26715 ("tcp: start receiver buffer autotuning sooner")
>     tried to decrease the threshold at which TCP auto-tuning starts
>     but it's doesn't work well in some environments
>     where the receiver has large MTU (9001) especially with high RTT
>     connections as in these environments rcvq_space.space will be the same
>     as rcv_wnd so TCP autotuning will never start because
>     sender can't send more than rcv_wnd size in one round trip.
>     To address this issue this patch is decreasing the initial
>     rcvq_space.space so TCP autotuning kicks in whenever the sender is
>     able to send more than 5360 bytes in one round trip regardless the
>     receiver's configured MTU.
> 
>     Fixes: a337531b942b ("tcp: up initial rmem to 128KB and SYN rwin to around 64KB")
>     Fixes: 041a14d26715 ("tcp: start receiver buffer autotuning sooner")
> 
> Signed-off-by: Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>

If the discussion concludes in favor of this patch please un-indent
this commit message, remove the empty line after the fixes tag, and 
repost.