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charset="us-ascii" Content-ID: <47565335DD75484C9728471FEB5A6018@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: f8a7e072-bb03-4104-8c54-08d73856d162 X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Sep 2019 14:29:43.2072 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: YbMcc29JW2W3F8jrAO/cdOWx3iRUJDMRdfYDJDkKxtiPW2N89xlDsnG8sYI07QCy X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR15MB1349 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.70,1.0.8 definitions=2019-09-13_07:2019-09-11,2019-09-13 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1011 bulkscore=0 malwarescore=0 suspectscore=0 impostorscore=0 lowpriorityscore=0 spamscore=0 priorityscore=1501 phishscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1909130144 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Sep 12, 2019 at 10:14:33AM +0100, Dave Taht wrote: > On Thu, Sep 12, 2019 at 1:59 AM Neal Cardwell wrot= e: > > > > On Wed, Sep 11, 2019 at 6:32 PM Thomas Higdon 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 > > > --- > > > > 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. >=20 > 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. >=20 > 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.