Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752100AbbFEVJ7 (ORCPT ); Fri, 5 Jun 2015 17:09:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53930 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751195AbbFEVJy (ORCPT ); Fri, 5 Jun 2015 17:09:54 -0400 Date: Fri, 5 Jun 2015 23:08:57 +0200 From: Oleg Nesterov To: Al Viro Cc: Linus Torvalds , Davidlohr Bueso , Peter Zijlstra , Paul McKenney , Tejun Heo , Ingo Molnar , Linux Kernel Mailing List , der.herr@hofr.at Subject: Re: [RFC][PATCH 0/5] Optimize percpu-rwsem Message-ID: <20150605210857.GA24905@redhat.com> References: <20150526114356.609107918@infradead.org> <1432665731.8196.3.camel@stgolabs.net> <20150605014558.GS7232@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150605014558.GS7232@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1106 Lines: 25 On 06/05, Al Viro wrote: > > FWIW, I hadn't really looked into stop_machine uses, but fs/locks.c one > is really not all that great - there we have a large trashcan of a list > (every file_lock on the system) and the only use of that list is /proc/locks > output generation. Sure, additions take this CPU's spinlock. And removals > take pretty much a random one - losing the timeslice and regaining it on > a different CPU is quite likely with the uses there. > > Why do we need a global lock there, anyway? Why not hold only one for > the chain currently being traversed? Sure, we'll need to get and drop > them in ->next() that way; so what? And note that fs/seq_file.c:seq_hlist_next_percpu() has no other users. And given that locks_delete_global_locks() takes the random lock anyway, perhaps the hashed lists/locking makes no sense, I dunno. Oleg. -- 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/