From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756482AbcBDArB (ORCPT ); Wed, 3 Feb 2016 19:47:01 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39106 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755494AbcBDAqv (ORCPT ); Wed, 3 Feb 2016 19:46:51 -0500 Subject: Re: [RFC][PATCH 0/3] Speed up SLUB poisoning + disable checks To: Christoph Lameter References: <1453770913-32287-1-git-send-email-labbott@fedoraproject.org> <20160126070320.GB28254@js1304-P5Q-DELUXE> <56B24B01.30306@redhat.com> <56B272B8.2050808@redhat.com> Cc: Kees Cook , Joonsoo Kim , Laura Abbott , Pekka Enberg , David Rientjes , Andrew Morton , Linux-MM , LKML , "kernel-hardening@lists.openwall.com" From: Laura Abbott Message-ID: <56B29F77.1010607@redhat.com> Date: Wed, 3 Feb 2016 16:46:47 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/03/2016 03:02 PM, Christoph Lameter wrote: >> The fast path uses the per cpu caches. No locks are taken and there >> is no IRQ disabling. For concurrency protection this comment >> explains it best: >> >> /* >> * The cmpxchg will only match if there was no additional >> * operation and if we are on the right processor. >> * >> * The cmpxchg does the following atomically (without lock >> * semantics!) >> * 1. Relocate first pointer to the current per cpu area. >> * 2. Verify that tid and freelist have not been changed >> * 3. If they were not changed replace tid and freelist >> * >> * Since this is without lock semantics the protection is only >> * against code executing on this cpu *not* from access by >> * other cpus. >> */ >> >> in the slow path, IRQs and locks have to be taken at the minimum. >> The debug options disable ever loading the per CPU caches so it >> always falls back to the slow path. > > You could add the use of per cpu lists to the slow paths as well in > order > to increase performance. Then weave in the debugging options. > How would that work? The use of the CPU caches is what defines the fast path so I'm not sure how to add them in on the slow path and not affect the fast path. > But the performance of the fast path is critical to the overall > performance of the kernel as a whole since this is a heavily used code > path for many subsystems. > I also notice that __CMPXCHG_DOUBLE is turned off when the debug options are turned on. I don't see any details about why. What's the reason for turning it off when the debug options are enabled? Thanks, Laura