From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758976AbZEFTCc (ORCPT ); Wed, 6 May 2009 15:02:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758627AbZEFTCT (ORCPT ); Wed, 6 May 2009 15:02:19 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:41448 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759554AbZEFTCR (ORCPT ); Wed, 6 May 2009 15:02:17 -0400 Date: Wed, 6 May 2009 12:02:16 -0700 From: "Paul E. McKenney" To: Andrew Morton Cc: Ingo Molnar , dhowells@redhat.com, linux-kernel@vger.kernel.org, niv@us.ibm.com, dvhltc@us.ibm.com, lethal@linux-sh.org, kernel@wantstofly.org, matthew@wil.cx Subject: Re: [PATCH] v4 RCU: the bloatwatch edition Message-ID: <20090506190216.GE6771@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090502163423.GA1633@linux.vnet.ibm.com> <20090506112459.5edd0902.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090506112459.5edd0902.akpm@linux-foundation.org> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 06, 2009 at 11:24:59AM -0700, Andrew Morton wrote: > On Wed, 6 May 2009 14:09:09 +0200 > Ingo Molnar wrote: > > > > > * David Howells wrote: > > > > > Paul E. McKenney wrote: > > > > > > > This patch is a version of RCU designed for (!SMP && EMBEDDED) > > > > provided as a proof of concept of a small-footprint RCU implementation. > > > > In particular, the implementation of synchronize_rcu() is extremely > > > > lightweight and high performance. It passes rcutorture testing in each > > > > of the four relevant configurations (combinations of NO_HZ and PREEMPT) > > > > on x86. This saves about 900 bytes compared to Classic RCU, and a > > > > couple kilobytes compared to Hierarchical RCU (updated to 2.6.29): > > > > ... > > > > Signed-off-by: Paul E. McKenney > > > > > > Acked-by: David Howells > > > > i'm wondering what Andrew thinks - he had objections, right? > > > > More like "concerns". It's unobvious to me that the modest .text > savings justify the costs of an additional RCU implementation. Where > those costs include > > - additional maintenance work and > > - the reduced code reliability which comes from fragmenting the > tester base. This will mostly affect users of the less popular RCU > implementations. > > But hey, maybe I'm wrong. And maybe I'm right, but we'll merge it anyway ;) ;-) How about if acceptance of Tiny RCU happens at the same time as Classic RCU is dropped? That would be a large net decrease in code size and complexity. Thanx, Paul