netdev - Re: [PATCH net] udp: don't be set unconnected if only UDP cmsg

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Message-ID: <CADaRJKtvGf_+aCx00KpJqz3gerBCWKvg+=PxcsTPSbLEhAwg8Q@mail.gmail.com>
Date: Tue, 16 Apr 2024 07:30:30 +0800
From: Yick Xie <yick.xie@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: willemb@...gle.com, netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net] udp: don't be set unconnected if only UDP cmsg

On Mon, Apr 15, 2024 at 10:11 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Yick Xie wrote:
> > If "udp_cmsg_send()" returned 0 (i.e. only UDP cmsg),
> > "connected" should not be set to 0. Otherwise it stops
> > the connected socket from using the cached route.
> >
> > Signed-off-by: Yick Xie <yick.xie@...il.com>
>
> This either needs to target net-next, or have
>
> Fixes: 2e8de8576343 ("udp: add gso segment cmsg")

I should have added that, sorry for the mess.

> I think it can be argued either way. This situation existed from the
> start, and is true for other cmsg that don't affect routing as well.
>
> If the impact of the route lookup is significant, it couls be argued
> to be a performance bug.

With sendmsg(), any smaller gso_size could be picked up dynamically.
Then it depends, "ip_route_output_flow()" could be as expensive as
"ip_make_skb()".

> I steer towards net-next. In which case it would be nice to also
> move the ipc.opt branch and perhaps even exclude other common cmsgs,
> such as SCM_TXTIME and SCM_TIMESTAMPING.

Both are fine. Though could it be better to take an easy backporting at first?