netdev - Re: [PATCH v4 2/2] tcp: Add snd_wnd to TCP

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Date:   Fri, 13 Sep 2019 14:28:33 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Thomas Higdon <tph@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Dave Jones <dsj@...com>, Eric Dumazet <edumazet@...gle.com>,
        Dave Taht <dave.taht@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH v4 2/2] tcp: Add snd_wnd to TCP_INFO

On Fri, Sep 13, 2019 at 2:02 PM Neal Cardwell <ncardwell@...gle.com> wrote:
>
> On Fri, Sep 13, 2019 at 3:36 PM Thomas Higdon <tph@...com> wrote:
> >
> > Neal Cardwell mentioned that snd_wnd would be useful for diagnosing TCP
> > performance problems --
> > > (1) Usually when we're diagnosing TCP performance problems, we do so
> > > from the sender, since the sender makes most of the
> > > performance-critical decisions (cwnd, pacing, TSO size, TSQ, etc).
> > > From the sender-side the thing that would be most useful is to see
> > > tp->snd_wnd, the receive window that the receiver has advertised to
> > > the sender.
> >
> > This serves the purpose of adding an additional __u32 to avoid the
> > would-be hole caused by the addition of the tcpi_rcvi_ooopack field.
> >
> > Signed-off-by: Thomas Higdon <tph@...com>
> > ---
> > changes from v3:
> >  - changed from rcv_wnd to snd_wnd
> >
> >  include/uapi/linux/tcp.h | 1 +
> >  net/ipv4/tcp.c           | 1 +
> >  2 files changed, 2 insertions(+)
> >
> > diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> > index 20237987ccc8..240654f22d98 100644
> > --- a/include/uapi/linux/tcp.h
> > +++ b/include/uapi/linux/tcp.h
> > @@ -272,6 +272,7 @@ struct tcp_info {
> >         __u32   tcpi_reord_seen;     /* reordering events seen */
> >
> >         __u32   tcpi_rcv_ooopack;    /* Out-of-order packets received */
> > +       __u32   tcpi_snd_wnd;        /* Remote peer's advertised recv window size */
> >  };
>
> Thanks for adding this!
>
> My run of ./scripts/checkpatch.pl is showing a warning on this line:
>
> WARNING: line over 80 characters
> #19: FILE: include/uapi/linux/tcp.h:273:
> +       __u32   tcpi_snd_wnd;        /* Remote peer's advertised recv
> window size */
>
> What if the comment is shortened up to fit in 80 columns and the units
> (bytes) are added, something like:
>
>         __u32   tcpi_snd_wnd;        /* peer's advertised recv window (bytes) */
just a thought: will tcpi_peer_rcv_wnd be more self-explanatory?
>
> neal