Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933229Ab0KLXx2 (ORCPT ); Fri, 12 Nov 2010 18:53:28 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:60613 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933008Ab0KLXx1 (ORCPT ); Fri, 12 Nov 2010 18:53:27 -0500 MIME-Version: 1.0 In-Reply-To: <20101112230650.GA3317@amd> References: <20101111080012.GB10210@amd> <20101112230650.GA3317@amd> From: Linus Torvalds Date: Fri, 12 Nov 2010 15:52:55 -0800 Message-ID: Subject: Re: [patches] seqlock: add barrier-less special cases for seqcounts To: Nick Piggin Cc: linux-kernel@vger.kernel.org, Al Viro , Ingo Molnar , Thomas Gleixner Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 999 Lines: 23 On Fri, Nov 12, 2010 at 3:06 PM, Nick Piggin wrote: . ... > seq2 = read_seqlock_begin(&child->d_seq); > if (read_seqcount_retry(&dentry->d_seq, seq)) > /* bail out */ So the only issue is that this particular back-to-back sequence with these kinds of "take one seqlock and release the previous one" where you currently end up having basically one smp_rmb() at the end of "read_seqlock_begin()", only to be followed immediately by another one starting out the "read_seqcount_retry()"? If so, I think we should make _that_ operation ("move from one seqlock to another") be the special one, because it smells like in general, using the special non-locking versions is going to be a very subtle interface. 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/