From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751408AbdJEQGY (ORCPT ); Thu, 5 Oct 2017 12:06:24 -0400 Received: from mx0a-00010702.pphosted.com ([148.163.156.75]:44136 "EHLO mx0b-00010702.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751286AbdJEQGW (ORCPT ); Thu, 5 Oct 2017 12:06:22 -0400 Date: Thu, 5 Oct 2017 11:05:35 -0500 From: Julia Cartwright To: Steven Rostedt CC: Thomas Gleixner , Arnaldo Carvalho de Melo , , , , Arnaldo Carvalho de Melo , Clark Williams , Dean Luick , Dennis Dalessandro , Doug Ledford , Kaike Wan , Leon Romanovsky , , Peter Zijlstra , Sebastian Andrzej Siewior , Sebastian Sanchez Subject: Re: [PATCH 1/2] IB/hfi1: Use preempt_{dis,en}able_nort() Message-ID: <20171005160535.GI647@jcartwri.amer.corp.natinst.com> References: <20171003154920.31566-1-acme@kernel.org> <20171003154920.31566-2-acme@kernel.org> <20171005141744.GC21185@jcartwri.amer.corp.natinst.com> <20171005153759.GG647@jcartwri.amer.corp.natinst.com> <20171005115539.7daafb66@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20171005115539.7daafb66@gandalf.local.home> User-Agent: Mutt/1.9.0 (2017-09-02) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-05_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_policy_notspam policy=outbound_policy score=30 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=30 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710050221 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 05, 2017 at 11:55:39AM -0400, Steven Rostedt wrote: > On Thu, 5 Oct 2017 10:37:59 -0500 > Julia Cartwright wrote: > > > On Thu, Oct 05, 2017 at 05:27:30PM +0200, Thomas Gleixner wrote: > > > On Thu, 5 Oct 2017, Julia Cartwright wrote: > > > > On Tue, Oct 03, 2017 at 12:49:19PM -0300, Arnaldo Carvalho de Melo wrote: > > > > > - preempt_disable(); > > > > > + preempt_disable_nort(); > > > > > this_cpu_inc(*sc->buffers_allocated); > > > > > > > > Have you tried this on RT w/ CONFIG_DEBUG_PREEMPT? I believe that the > > > > this_cpu_* operations perform a preemption check, which we'd trip. > > > > > > Good point. Changing this to migrate_disable() would do the trick. > > > > Wouldn't we still trip the preempt check even with migration disabled? > > In another thread I asked the same question: should the preemption > > checks here be converted to migration-checks in RT? > > Is it a "preemption check"? Sorry if I was unclear, more precisely: the this_cpu_* family of accessors, w/ CONFIG_DEBUG_PREEMPT currently spits out a warning when the caller is invoked in a context where preemption is enabled. The check is shared w/ the smp_processor_id() check, as implemented in lib/smp_processor_id.c. It effectively boils down to a check of preempt_count() and irqs_disabled(). > Getting a cpu # should only care about migration. I think we're agreeing? :) > This isn't the same as a rcu_sched check is it? That does care about > preemption. This is something totally different, I think. Julia