Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966127AbaFSXHh (ORCPT ); Thu, 19 Jun 2014 19:07:37 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:44333 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964958AbaFSXHg (ORCPT ); Thu, 19 Jun 2014 19:07:36 -0400 Date: Thu, 19 Jun 2014 16:07:32 -0700 From: "Paul E. McKenney" To: josh@joshtriplett.org Cc: Christoph Lameter , Andi Kleen , Dave Hansen , LKML , "Chen, Tim C" Subject: Re: [bisected] pre-3.16 regression on open() scalability Message-ID: <20140619230732.GX4904@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140618203052.GT4669@linux.vnet.ibm.com> <20140618235131.GA25946@linux.vnet.ibm.com> <20140619014200.GO8178@tassilo.jf.intel.com> <20140619180916.GE4904@linux.vnet.ibm.com> <20140619204220.GJ4904@linux.vnet.ibm.com> <20140619213203.GA16747@cloud> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140619213203.GA16747@cloud> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14061923-6688-0000-0000-000002AFC70D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 19, 2014 at 02:32:03PM -0700, josh@joshtriplett.org wrote: > On Thu, Jun 19, 2014 at 04:16:34PM -0500, Christoph Lameter wrote: > > This looks very much like the CONFIG_PREEMPT problem in not so > > extreme form. Maybe we need to add another config option: > > > > CONFIG_REALLY_REALLY_NO_PREEMPT > > > > to get the fastest code possible and those cond_rescheds removed from the > > critical paths? > > > > Or better > > > > CONFIG_PREEMPT_HALF_WAY > > > > to enable those cond_rescheds. > > That much actually does seem quite reasonable: making cond_resched() do > non-trivial work ought to have a config option to disable it. I am putting together patches based on Eric Dumazet's suggestion and on a variant of the above approach. However, I do expect the distros to starve to death between those two bales of hay. But perhaps the actual patches will inspire a bit of light to go with this thread's heat and smoke. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/