From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752638AbbCGOJe (ORCPT ); Sat, 7 Mar 2015 09:09:34 -0500 Received: from mail-qc0-f175.google.com ([209.85.216.175]:40576 "EHLO mail-qc0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750960AbbCGOJc (ORCPT ); Sat, 7 Mar 2015 09:09:32 -0500 Date: Sat, 7 Mar 2015 09:09:27 -0500 From: Jeff Layton To: Daniel Wagner Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Viro , "J. Bruce Fields" , Andi Kleen Subject: Re: [PATCH v3 0/2] Use blocked_lock_lock only to protect blocked_hash Message-ID: <20150307090927.3a37c201@tlielax.poochiereds.net> In-Reply-To: <20150307090041.16fbf4f8@tlielax.poochiereds.net> References: <1425628412-30259-1-git-send-email-daniel.wagner@bmw-carit.de> <20150307090041.16fbf4f8@tlielax.poochiereds.net> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.26; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 7 Mar 2015 09:00:41 -0500 Jeff Layton wrote: > On Fri, 6 Mar 2015 08:53:30 +0100 > Daniel Wagner wrote: > > > Hi, > > > > Finally, I got a bigger machine and did a quick test round. I expected > > to see some improvements but the resutls do not show any real gain. So > > they are merely refactoring patches. > > > > Ok, in that case is there any point in merging these? I'm all for > breaking up global locks when it makes sense, but if you can't > demonstrate a clear benefit then I'm less inclined to take the churn. > > Perhaps we should wait to see if a benefit emerges when/if you convert > the lglock code to use normal spinlocks (like Andi suggested)? That > seems like a rather simple conversion, and I don't think it's > "cheating" in any sense of the word. > > I do however wonder why Nick used arch_spinlock_t there when he wrote > the lglock code instead of normal spinlocks. Was it simply memory usage > considerations or something else? > Hmm...to answer my own question. The (old) LWN article here seems to suggest that he did it that way to avoid preemption: http://lwn.net/Articles/401738/ I don't think we need to avoid being preempted in the file-locking code, but I'm not sure about stop_machine.c. Is that necessary there? The comment in queue_stop_cpus_work seems to indicate that it may be. -- Jeff Layton