Re: [PATCH 1/2] tcp: leverage support of SO_PEEK_OFF socket option when available

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Apr 23, 2024 at 07:50:10PM +0200, Stefano Brivio wrote:
> On Sat, 20 Apr 2024 15:19:19 -0400
> Jon Maloy <jmaloy@redhat.com> wrote:
[snip]
> > +	set_peek_offset(s, 0);
> 
> Do we really need to initialise it to zero on a new connection? Extra
> system calls on this path matter for latency of connection
> establishment.

Sort of, yes: we need to enable the SO_PEEK_OFF behaviour by setting
it to 0, rather than the default -1.  We could lazily enable it, but
we'd need either to a) do it later in the handshake (maybe when we set
ESTABLISHED), but we'd need to be careful it is always set before the
first MSG_PEEK or b) keep track of whether it's set on a per-socket
basis (this would have the advantage of robustness if we ever
encountered a kernel that weirdly allows it for some but not all TCP
sockets).

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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