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From:   Ivan Babrou <ivan@cloudflare.com>
Date:   Wed, 5 Jan 2022 20:20:06 -0800
Message-ID: <CABWYdi2oapjDMSJb+8T7BXMM6h+ftCQCSpPPePXaS3MyS4hD+w@mail.gmail.com>
Subject: Re: [PATCH net] tcp: note that tcp_rmem[1] has a limited range
To:     Eric Dumazet <edumazet@google.com>
Cc:     Stephen Hemminger <stephen@networkplumber.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@cloudflare.com>,
        "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>
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On Tue, Jan 4, 2022 at 12:33 AM Eric Dumazet <edumazet@google.com> wrote:
> I guess you have to define what is the initial window.

What I mean here is the first window after scaling is allowed, so the
one that appears in the first non-SYN ACK.

> There seems to be a confusion between rcv_ssthresh and sk_rcvbuf
>
> If you want to document what is rcv_ssthresh and how it relates to sk_rcvbuf,
> you probably need more than few lines in Documentation/networking/ip-sysctl.rst

I can't say I fully understand how buffer sizes grow and how
rcv_ssthresh and sk_rcvbuf interact to document this properly.

All I want is to document the fact that no matter what you punch into
sysctls, you'll end up with an initial scaled window (defined above)
that's no higher than 64k. Let me know if this is incorrect and if
there's a way we can put this into words without going into too much
detail.

> Please do not. We set this sysctl to 0.5 MB
> DRS is known to have quantization artifacts.

Where can I read more about the quantization artifacts you mentioned?