From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755621AbbJUPfJ (ORCPT ); Wed, 21 Oct 2015 11:35:09 -0400 Received: from mail-wi0-f173.google.com ([209.85.212.173]:38273 "EHLO mail-wi0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755491AbbJUPfC (ORCPT ); Wed, 21 Oct 2015 11:35:02 -0400 Date: Wed, 21 Oct 2015 17:35:01 +0200 From: Frederic Weisbecker To: Christoph Lameter Cc: Chris Metcalf , Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Peter Zijlstra , Andrew Morton , Rik van Riel , Tejun Heo , Thomas Gleixner , "Paul E. McKenney" , Viresh Kumar , Catalin Marinas , Will Deacon , Andy Lutomirski , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v8 08/14] nohz_full: allow disabling the 1Hz minimum tick at boot Message-ID: <20151021153400.GA19230@lerouge> References: <1445373372-6567-1-git-send-email-cmetcalf@ezchip.com> <1445373372-6567-9-git-send-email-cmetcalf@ezchip.com> <20151020210331.GC29289@lerouge> 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, Oct 21, 2015 at 09:28:04AM -0500, Christoph Lameter wrote: > On Tue, 20 Oct 2015, Frederic Weisbecker wrote: > > > There have been proposals to disable/tune the 1 Hz tick via debugfs which > > I Nacked because once you give such an opportunity to the users, they > > will use that hack and never fix the real underlying issue. > > Well this is a pretty bad argument. By that reasoning no one should be > allowed to use root. After all stupid users will become root and kill > processes that are hung. And the underlying issue that causes those hangs > in processes will never be fixed because they will keep on killing > processes. I disagree. There is an signifiant frontier between: _ hack it up and you're responsible of the consequences, yourself and _ provide a buggy hack to the user and support this officially upstream Especially as all I've seen in two years, wrt. solving the 1 Hz issue, is patches like this. Almost nobody really tried to dig into the real issues that are well known and identified after all now, and not that hard to fix: it's many standalone issues to make the scheduler resilient with full-total-hard-dynticks. The only effort toward that I've seen lately is: https://lkml.org/lkml/2015/10/14/192 and still I think the author came to that nohz issue by accident. Many users are too easily happy with hacks like this and that one is a too much a good opportunity for them.