From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934040AbcATObY (ORCPT ); Wed, 20 Jan 2016 09:31:24 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:35415 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933376AbcATObW (ORCPT ); Wed, 20 Jan 2016 09:31:22 -0500 Date: Wed, 20 Jan 2016 15:31:19 +0100 From: Frederic Weisbecker To: Thomas Gleixner Cc: Peter Zijlstra , LKML , Byungchul Park , Chris Metcalf , Luiz Capitulino , Christoph Lameter , "Paul E . McKenney" , Mike Galbraith , Rik van Riel Subject: Re: [RFC PATCH 4/4] sched: Upload nohz full CPU load on task enqueue/dequeue Message-ID: <20160120143117.GA22723@lerouge> References: <1452700891-21807-1-git-send-email-fweisbec@gmail.com> <1452700891-21807-5-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 20, 2016 at 10:03:32AM +0100, Thomas Gleixner wrote: > On Wed, 13 Jan 2016, Frederic Weisbecker wrote: > > A solution to fix this is to update the CPU load everytime we enqueue > > or dequeue a task in the fair runqueue and more than a jiffy occured > > since the last update. > > That's not a solution. That's just crap. Have you seen the "RFC"? That's what we use when we are not yet confident with a solution but we want to start a debate in order to find a proper one. > > I tell you since years, that you need to fix that remote accounting stuff, > but no, you insist on adding more trainwrecks left and right. The solution you proposed to me was to do remote scheduler_tick() from CPU 0 and this was nacked by peterz (and he was right). We all know that we need to fix this remote accounting stuff, but I'm the only one who actually _tries_, at least through RFC's to start discussions, such that I find the right direction to move forward. You're not helping me _at all_ with your shitty rants, all you're doing is discouraging me and pushing me out to quit kernel development. I seriously thought about it but that's not going to happen, unless there is a collective opinion toward the fact I'm a nuisance for the community. So go to hell Thomas! > > > The problem with doing this remotely is that we can miss past cpu loads if > > there was several enqueue/dequeue operations happening while tickless. > > That's complete bullshit. > > 1) How is remote accounting that happens every tick different from local > accounting which happens every tick? Enqueue/dequeue don't happen on tick, unless there is a wakeup on that interrupt. > > 2) How do you have enqueue/dequeue operations when you are running in full > nohz, i.e. one task is consuming 100% cpu time in user space? Well that task is going to sleep, wake up, sleep like any other task. We need to account these slices properly. If a second task wakes up and restart the tick, we must make sure that the previous tickless frame got accounted properly. Besides, if a SCHED_FIFO task runs (tickless) with SCHED_NORMAL tasks in the runqueue, those are typically still accounted with the tick, so perhaps we need to keep that behaviour without the tick as well and account those SCHED_NORMAL task's load. > > I'm really tired of that tinkering. The proper solution is to make NOHZ_FULL > depend on BROKEN. Sure, knock yourself out. > > Thanks, > > tglx