From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 28 May 2002 12:22:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 28 May 2002 12:22:33 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.101]:2291 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id ; Tue, 28 May 2002 12:22:31 -0400 Date: Tue, 28 May 2002 21:55:35 +0530 From: Dipankar Sarma To: Robert Love Cc: "David S. Miller" , Linus Torvalds , linux-kernel@vger.kernel.org, Paul McKenney , Andrea Arcangeli Subject: Re: 8-CPU (SMP) #s for lockfree rtcache Message-ID: <20020528215535.A22328@in.ibm.com> Reply-To: dipankar@in.ibm.com In-Reply-To: <20020528171104.D19734@in.ibm.com> <20020528.042514.92633856.davem@redhat.com> <20020528182806.A21303@in.ibm.com> <1022600998.20317.44.camel@sinai> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi Robert, On Tue, May 28, 2002 at 08:49:58AM -0700, Robert Love wrote: > > > Well, the last time RCU was discussed, Linus said that he would > > like to see someplace where RCU clearly helps. > > I agree the numbers posted are nice, but I remain skeptical like Linus. > Sure, the locking overhead is nearly gone in the profiled function where > RCU is used. But the overhead has just been _moved_ to wherever the RCU > work is now done. Any benchmark needs to include the damage done there, > too. Have you looked at the rt_rcu patch ? Where do you think there is overhead compared to what route cache alread does ? In my profiles, rcu routines and kernel mechanisms that it uses don't show high up. If you have any suggestions, then I can do an investigation. > > I also balk at implicit locking... > I agree that it is better to keep things simple and RCU isn't a replacement for locking. However the route cache hash table with refcount is a relatively simpler use of RCU and since it has benefits, we shouldn't shy away from using it if it is useful. Thanks -- Dipankar Sarma http://lse.sourceforge.net Linux Technology Center, IBM Software Lab, Bangalore, India.