From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66720C43142 for ; Tue, 26 Jun 2018 19:27:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 06CFD26B4A for ; Tue, 26 Jun 2018 19:27:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Te0Oc3/W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06CFD26B4A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752647AbeFZT1u (ORCPT ); Tue, 26 Jun 2018 15:27:50 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:59906 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750907AbeFZT1s (ORCPT ); Tue, 26 Jun 2018 15:27:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=N+sopYf2CE+gPMZbtFcxCgUf5l/4mnkBWEBnbcgwMJA=; b=Te0Oc3/WAuy0n30l8wN1uvRov Q9eWEw9ttZ7vUdxJAB1L3/k+ptjn/+CayF54UELWUEQ2OZ9cAJ+O4ivKRvFm1c801/Eo4/JYztORg u6q5p/UhH3kIygav1KYyh1kp1KRaUsI5/EC12YPlk4JfjFPEgIOAZbWuvvOYaK28qXynhI8r/0o3a POQtr8Yxce7JMEstGZsXlO1j9XlHbf6bvCLrFtz7MPCpyxqGkIpM8Sb8rp3fbMs3rAV/n6I/QoSEx DKC2NUPqG4/uEOiTpCDJhqIGewROKN3U+v7hRcMlgwStNR+Hnq548tYdk6m+mw9SI8J0ChIXa+stb /fGL2vqeg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fXtcg-000558-Bd; Tue, 26 Jun 2018 19:27:30 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 931382029FA0A; Tue, 26 Jun 2018 21:27:28 +0200 (CEST) Date: Tue, 26 Jun 2018 21:27:28 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how rcu_seq_snap works Message-ID: <20180626192728.GN2494@hirez.programming.kicks-ass.net> References: <20180626003448.GA26209@linux.vnet.ibm.com> <20180626003513.27812-16-paulmck@linux.vnet.ibm.com> <20180626173055.GJ2494@hirez.programming.kicks-ass.net> <20180626181025.GF3593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180626181025.GF3593@linux.vnet.ibm.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 26, 2018 at 11:10:25AM -0700, Paul E. McKenney wrote: > > Is the below not much simpler: > > > > > static inline unsigned long rcu_seq_snap(unsigned long *sp) > > > { > > > unsigned long s; > > > > s = smp_load_aquire(sp); > > > > /* Add one GP */ > > s += 1 << RCU_SEQ_CTR_SHIFT; > > > > /* Complete any pending state by rounding up */ > > s = __ALIGN_MASK(s, RCU_SEQ_STATE_MASK); > > > > return s; > > } > > Seems equivalent to me, but with more lines. To say nothing of more > levels of lookup of macro definitions. ;-) But it does explain the various parts in the equation, or at least gives a fair clue as to how the thing composes. And I find the alignment thing far easier to read that an open coded variant, but whatever.