On Fri, Sep 13, 2019 at 10:29 AM Thomas Higdon <t...@fb.com> wrote: > > On Thu, Sep 12, 2019 at 10:14:33AM +0100, Dave Taht wrote: > > On Thu, Sep 12, 2019 at 1:59 AM Neal Cardwell <ncardw...@google.com> wrote: > > > > > > On Wed, Sep 11, 2019 at 6:32 PM Thomas Higdon <t...@fb.com> wrote: > > > > > > > > Neal Cardwell mentioned that rcv_wnd would be useful for helping > > > > diagnose whether a flow is receive-window-limited at a given instant. > > > > > > > > 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 <t...@fb.com> > > > > --- > > > > > > Thanks, Thomas. > > > > > > I know that when I mentioned this before I mentioned the idea of both > > > tp->snd_wnd (send-side receive window) and tp->rcv_wnd (receive-side > > > receive window) in tcp_info, and did not express a preference between > > > the two. Now that we are faced with a decision between the two, > > > personally I think it would be a little more useful to start with > > > tp->snd_wnd. :-) > > > > > > Two main reasons: > > > > > > (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. > > > > I am under the impression, that particularly in the mobile space, that > > network behavior > > is often governed by rcv_wnd. At least, there's been so many papers on > > this that I'd > > tended to assume so. > > > > Given a desire to do both vars, is there a *third* u32 we could add to > > fill in the next hole? :) > > ecn marks? > > Neal makes some good points -- there is a fair amount of existing > information for deriving receive window. It seems like snd_wnd would be > more valuable at this moment. For the purpose of pairing up these __u32s > to get something we can commit, I propose that we go with > the rcv_ooopack/snd_wnd pair for now, and when something comes up later, > one might consider pairing up rcv_wnd.
FWIW that sounds like a great plan to me. Thanks, Thomas! neal
