From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755679AbZEFScL (ORCPT ); Wed, 6 May 2009 14:32:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758959AbZEFSbj (ORCPT ); Wed, 6 May 2009 14:31:39 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:46969 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755690AbZEFSbh (ORCPT ); Wed, 6 May 2009 14:31:37 -0400 Date: Wed, 6 May 2009 11:24:59 -0700 From: Andrew Morton To: Ingo Molnar Cc: dhowells@redhat.com, paulmck@linux.vnet.ibm.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: <20090506112459.5edd0902.akpm@linux-foundation.org> In-Reply-To: <20090506120909.GR25203@elte.hu> References: <20090502163423.GA1633@linux.vnet.ibm.com> <12234.1241558327@redhat.com> <20090506120909.GR25203@elte.hu> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ;)