From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752390AbdIKC4X convert rfc822-to-8bit (ORCPT ); Sun, 10 Sep 2017 22:56:23 -0400 Received: from mout.gmx.net ([212.227.15.19]:58302 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752139AbdIKC4W (ORCPT ); Sun, 10 Sep 2017 22:56:22 -0400 Message-ID: <1505098524.18240.42.camel@gmx.de> Subject: Re: [lkp-robot] [sched/fair] 6d46bd3d97: netperf.Throughput_tps -11.3% regression From: Mike Galbraith To: Joel Fernandes , kernel test robot Cc: LKML , Peter Zijlstra , Josef Bacik , Juri Lelli , Brendan Jackman , Dietmar Eggemann , Matt Fleming , Rik van Riel , Ingo Molnar , lkp@01.org Date: Mon, 11 Sep 2017 04:55:24 +0200 In-Reply-To: References: <20170827010226.19703-1-joelaf@google.com> <20170910134021.GB29265@yexl-desktop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 Mime-Version: 1.0 Content-Transfer-Encoding: 8BIT X-Provags-ID: V03:K0:r3W2iQr8Q88FRGkcVi5wJrYGUJ0c6sBv4+DDKiA9BJQkhdbwQIi wfT0YC2+ZfJAy9EKF1LiVDp9BMq99mQdKvvbOSUU9FRNuvpTgYf/pVLkvScxz3iRdxu1yab XtKpseXCB5d5Y33zW8ecvEeKQ7K6rUZ7ORpQsFeCpAjK7GZZSqJqyC8lc7jrcm7sNJl91wR QXLFoAl2ws8zllXDudP2A== X-UI-Out-Filterresults: notjunk:1;V01:K0:ThrLpErEljo=:dDPVyruxZ853ceVuyJ5KfF vkqICUCZCShAWF8mjGHXNcs8/1gQ8OwtmlHBuYN6r1Jx0XcRJyNYYbmIjZy9kUFS3lUeHVs/z ZS2vMBq61fRtLtGUgGOBWaEc+YZJwOhSlBIfyhqnxFnS/15UjsIt1vxqeCdcUnX7LqjuyYrbk YVMVPd3HXcO9J7aV6shlbmNSHQj2UuG4mMP3lwSSO5wgwCgtQnS7YqMa63qhWg4G+fhUnlTIu tY/UCqMzvUf5eU0IxlvjaieKSV+nyC7qLJil1pboY2udgUNoS0oRUTvxpO8rjYWFh6uyTVvI/ v71iLRwbf6ZpQmsjftszGdysmJ4w0BT+3KkWlB4BfBTpgwCBBr6zC+j5PSn74b5w27yMBfWpW dVpKzhgkDIvXg9CasBHocQzVuwWp/E8Kjs8c8i8OwqXzK889xdAfCBbGyqDlIRXy07h5pKjRc /xb2M/Ij9Gvij+fFbgeFfMA4I6hdAxbEBdSy4kNCuu9X3k/7vz8oPdA7Dn7Hzo0BHcUH+3rv0 R+hTCy6zFK9ivAos6SIl3ZwvgT3lEb5u2+eZe2uaK0HGi21MIW6DfK8DIO3wtPttPR0B1Lo2H wHrD+et23r7kP19LB+veWPQbPny7MvLWsy5hmnxqNsFyJP6ZcHMkod101s/D9dhjKRdah8q3d GiQhwri4JZEM2lXUD5AIXxW3QOPr53UA0DLsqVZhMrsEgui7ykCyLtu6ThTGt8+DafAxvvZDr X2B9a7WTq3oL2x+FkMeE2Wic7h5ezOn+wd6AU8k5TFcXPSuxSmPZxdUSVSkoDgwElXRK1RI07 gu5nuUsxxEvJNvkZKG5AuCBgTPYpPa96KyMB9r9oXASS7IO6sA= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2017-09-10 at 09:53 -0700, Joel Fernandes wrote: > > Anyone know what in the netperf test triggers use of the sync flag? homer:..kernel/linux-master # git grep wake_up_interruptible_sync_poll net net/core/sock.c: wake_up_interruptible_sync_poll(&wq->wait, POLLIN | POLLPRI | net/core/sock.c: wake_up_interruptible_sync_poll(&wq->wait, POLLOUT | net/sctp/socket.c: wake_up_interruptible_sync_poll(&wq->wait, POLLIN | net/smc/smc_rx.c: wake_up_interruptible_sync_poll(&wq->wait, POLLIN | POLLPRI | net/tipc/socket.c: wake_up_interruptible_sync_poll(&wq->wait, POLLOUT | net/tipc/socket.c: wake_up_interruptible_sync_poll(&wq->wait, POLLIN | net/unix/af_unix.c: wake_up_interruptible_sync_poll(&wq->wait, net/unix/af_unix.c: wake_up_interruptible_sync_poll(&u->peer_wait, The same as metric tons of other stuff. Once upon a time, we had avg_overlap to help decide whether to wake core affine or not, on top of the wake_affine() imbalance constraint, but instrumentation showed it to be too error prone, so it had to die.  These days, an affine wakeup generally means cache affine, and the sync hint gives you a wee bit more chance of migration near to tasty hot data being approved. The sync hint was born back in the bad old days, when communicating tasks not sharing L2 may as well have been talking over two tin cans and a limp string.  These days, things are oodles better, but truly synchronous stuff could still benefit from core affinity (up to hugely for very fast/light stuff) if it weren't for all the caveats that can lead to tossing concurrency opportunities out the window. -Mike