netdev - Re: [PATCH net-next v2] tcp: up initial rmem to 128KB and SYN rwin to around 64KB

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Date:   Mon, 1 Oct 2018 15:18:11 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next v2] tcp: up initial rmem to 128KB and SYN rwin to
 around 64KB

On Sat, Sep 29, 2018 at 11:23 AM, David Miller <davem@...emloft.net> wrote:
>
> From: Yuchung Cheng <ycheng@...gle.com>
> Date: Fri, 28 Sep 2018 13:09:02 -0700
>
> > Previously TCP initial receive buffer is ~87KB by default and
> > the initial receive window is ~29KB (20 MSS). This patch changes
> > the two numbers to 128KB and ~64KB (rounding down to the multiples
> > of MSS) respectively. The patch also simplifies the calculations s.t.
> > the two numbers are directly controlled by sysctl tcp_rmem[1]:
> >
> >   1) Initial receiver buffer budget (sk_rcvbuf): while this should
> >      be configured via sysctl tcp_rmem[1], previously tcp_fixup_rcvbuf()
> >      always override and set a larger size when a new connection
> >      establishes.
> >
> >   2) Initial receive window in SYN: previously it is set to 20
> >      packets if MSS <= 1460. The number 20 was based on the initial
> >      congestion window of 10: the receiver needs twice amount to
> >      avoid being limited by the receive window upon out-of-order
> >      delivery in the first window burst. But since this only
> >      applies if the receiving MSS <= 1460, connection using large MTU
> >      (e.g. to utilize receiver zero-copy) may be limited by the
> >      receive window.
> >
> > This patch also lowers the initial bytes expected to receive in
> > the receiver buffer autotuning algorithm - otherwise the receiver
> > may take two to three rounds to increase the buffer to the
> > appropriate level (2x sender congestion window).
> >
> > With this patch TCP memory configuration is more straight-forward and
> > more properly sized to modern high-speed networks by default. Several
> > popular stacks have been announcing 64KB rwin in SYNs as well.
> >
> > Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> > Signed-off-by: Wei Wang <weiwan@...gle.com>
> > Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Reviewed-by: Soheil Hassas Yeganeh <soheil@...gle.com>
>
> Applied, thanks.

Hi David: thanks for taking this patch - I didn't notice this earlier
but it seems patch v1 was applied instead of v2? should I submit a
v2-v1-diff patch?