From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756285AbbCFTzN (ORCPT ); Fri, 6 Mar 2015 14:55:13 -0500 Received: from cantor2.suse.de ([195.135.220.15]:34032 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753787AbbCFTzK (ORCPT ); Fri, 6 Mar 2015 14:55:10 -0500 Message-ID: <1425671702.19505.54.camel@stgolabs.net> Subject: Re: sched: softlockups in multi_cpu_stop From: Davidlohr Bueso To: Linus Torvalds Cc: Jason Low , Ingo Molnar , Sasha Levin , Peter Zijlstra , LKML , Dave Jones Date: Fri, 06 Mar 2015 11:55:02 -0800 In-Reply-To: References: <54F41516.6060608@oracle.com> <54F98F1F.3080107@oracle.com> <20150306123233.GA9972@gmail.com> <1425662342.19505.41.camel@stgolabs.net> <1425668223.2475.94.camel@j-VirtualBox> <1425669643.19505.46.camel@stgolabs.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2015-03-06 at 11:32 -0800, Linus Torvalds wrote: > IOW, I wonder if we could special-case the common non-IO > fault-handling path something along the lines of: > > - look up the vma in the vma lookup cache But you'd still need mmap_sem there to at least get the VMA's first value. > - look up the page in the page cache > - get the page table spinlock > - re-check the vma now (it ends up being stable if it can't be torn > down due to the page table spinlock) > > because I suspect that page faults are the biggest users of that > mmap_sem, and we could probably handle a fairly large common case > (making it simpler by special-casing it and punting in any even > _slightly_ complicated situations) without even getting the semaphore > at all, since we have to serialize on the actual page table *anyway*. > > Basically, to me, the whole "if a lock is so contended that we need to > play locking games, then we should look at why we *use* the lock, > rather than at the lock itself" is a religion. > > Linus > -- > 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/