netdev - Re: [PATCH net-next 3/3] tcp: derive delack_max from rto

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Date: Fri, 22 Sep 2023 12:53:19 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: David Laight <David.Laight@...lab.com>
Cc: David Ahern <dsahern@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Yuchung Cheng <ycheng@...gle.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next 3/3] tcp: derive delack_max from rto_min

On Fri, Sep 22, 2023 at 11:59 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Eric Dumazet
> > Sent: 21 September 2023 13:58
> >
> > On Thu, Sep 21, 2023 at 2:37 PM David Ahern <dsahern@...nel.org> wrote:
> > >
> >
> > > My comment is solely about mismatch on data types. I am surprised use of
> > > max_t with mixed data types does not throw a compiler warning.
> >
> > This was intentional.
> >
> > This is max_t() purpose really.
>
> Apart from when it gets used to accidentally mask high bits :-)
> (Although hat is usually consigned to min_t()).

As explained, this is not an accident, but a conscious decision I made.

>
> Here
>         u32 delack_from_rto_min = max(rto_min, 2u) - 1;
> would probably be safer (as in have no casts that might have
> unwanted side effects).
>

I find my solution more readable.

max(-1, 1) is 1.

If this was not the case, many things would be broken in the kernel.