From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932852Ab3HGT2r (ORCPT ); Wed, 7 Aug 2013 15:28:47 -0400 Received: from terminus.zytor.com ([198.137.202.10]:53000 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755753Ab3HGT2p (ORCPT ); Wed, 7 Aug 2013 15:28:45 -0400 User-Agent: K-9 Mail for Android In-Reply-To: References: <20130807173606.872055511@goodmis.org> <1375898048.6848.18.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [RFC][PATCH 3/2] x86/jump labels: Count and display the short jumps used From: "H. Peter Anvin" Date: Wed, 07 Aug 2013 12:27:51 -0700 To: Linus Torvalds , Steven Rostedt CC: Linux Kernel Mailing List , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Jason Baron Message-ID: <2e3a4a90-2915-4b75-b807-b0e802e4955f@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Well we do... both to extract relocations and to sort the exception table. Perhaps we need to merge those kinds of postprocessing tools? Linus Torvalds wrote: >On Wed, Aug 7, 2013 at 10:54 AM, Steven Rostedt >wrote: >> >> On another box, using a distro config, I had even better results: >> >> [ 2.352448] short jumps: 193 >> [ 2.355407] long jumps: 219 > >.. well, another way of looking at this is to say that all of this >effort saves just 579 bytes. > >Yes, maybe some of those bytes are in really hot paths, but the other >side of *that* coin is that the 2-vs-5 byte jump doesn't much matter >if it's already cached. > >So I'd vote for not doing this. If we had some simple way to do the >short jumps, I think it would be lovely. Or if we had to parse the ELF >files and do instruction rewriting for various other reasons, and the >jump rewriting was just one small detail. > >But using 576 new lines (the diffstat for your patch 1/2 that adds the >infrastructure to do the rewriting) in order to same just about >exactly that many bytes in the binary - the effort just doesn't work >out, imnsho. > > Linus -- Sent from my mobile phone. Please excuse brevity and lack of formatting.