From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933596AbbBCIkh (ORCPT ); Tue, 3 Feb 2015 03:40:37 -0500 Received: from shards.monkeyblade.net ([149.20.54.216]:51793 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932575AbbBCIke (ORCPT ); Tue, 3 Feb 2015 03:40:34 -0500 Date: Tue, 03 Feb 2015 00:40:31 -0800 (PST) Message-Id: <20150203.004031.593368249759204527.davem@davemloft.net> To: akpm@linux-foundation.org Cc: Yalin.Wang@sonymobile.com, kirill@shutemov.name, arnd@arndb.de, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC] change non-atomic bitops method From: David Miller In-Reply-To: <20150202223851.f30768d0.akpm@linux-foundation.org> References: <35FD53F367049845BC99AC72306C23D1044A02027E0B@CNBJMBX05.corpusers.net> <35FD53F367049845BC99AC72306C23D1044A02027E0C@CNBJMBX05.corpusers.net> <20150202223851.f30768d0.akpm@linux-foundation.org> X-Mailer: Mew version 6.5 on Emacs 24.1 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.7 (shards.monkeyblade.net [149.20.54.216]); Tue, 03 Feb 2015 00:40:34 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrew Morton Date: Mon, 2 Feb 2015 22:38:51 -0800 > It is only with both these ratios that we can work out whether the > patch is a net gain. My suspicion is that set_bit on an already-set > bit is so rare that the patch will be a loss. A common pattern is implementing a "referenced" bit, and in that case the bit is often already set, and in such a scenerio the proposed change is a huge win.