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

[Jon Maloy <jmaloy@redhat.com>]

On 2024-04-23 20:48, David Gibson wrote:
> 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.
Yes. Although I moved it to  tcp_conn_from_tap() in the next version,
to make it more symmetric with the one in tcp_tap_conn_from_sock()
> 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).
>