From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752153AbXINHAq (ORCPT ); Fri, 14 Sep 2007 03:00:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750868AbXINHAi (ORCPT ); Fri, 14 Sep 2007 03:00:38 -0400 Received: from brick.kernel.dk ([87.55.233.238]:24313 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751277AbXINHAi (ORCPT ); Fri, 14 Sep 2007 03:00:38 -0400 Date: Fri, 14 Sep 2007 09:00:20 +0200 From: Jens Axboe To: Nick Piggin Cc: Linux Kernel Mailing List , Linus Torvalds Subject: Re: [patch] shared tag queue barrier comment Message-ID: <20070914070020.GU25592@kernel.dk> References: <20070914064112.GA25277@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070914064112.GA25277@wotan.suse.de> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 14 2007, Nick Piggin wrote: > > Should add some comments for the tag barriers (they won't be so important > if we can switch over to the explicit _lock bitops, but for now we should > make it clear). Thanks! > Jens' original patch said a barrier after the test_and_clear_bit was also > required. I can't see why (and it would prevent the use of the _lock bitop). Yeah, I don't think it's needed either. The important bit was ordering the ->tag_index[tag] = NULL setting before clearing the bit, and as long as those two operations are ordered, we are good to go. So the last memory barrier was not needed. -- Jens Axboe