From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751135AbdFAL6X (ORCPT ); Thu, 1 Jun 2017 07:58:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48630 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054AbdFAL6W (ORCPT ); Thu, 1 Jun 2017 07:58:22 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A4E7637EEB Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx05.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jpoimboe@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com A4E7637EEB Date: Thu, 1 Jun 2017 06:58:20 -0500 From: Josh Poimboeuf To: Ingo Molnar Cc: x86@kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Linus Torvalds , Andy Lutomirski , Jiri Slaby , "H. Peter Anvin" , Peter Zijlstra Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder Message-ID: <20170601115819.3twoowcnvtrfzjzr@treble> References: <20170601060824.wv2go3adbvx5ptmt@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170601060824.wv2go3adbvx5ptmt@gmail.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 01 Jun 2017 11:58:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 01, 2017 at 08:08:24AM +0200, Ingo Molnar wrote: > > * Josh Poimboeuf wrote: > > > Here's the contents of the undwarf.txt file which explains the 'why' in > > more detail: > > Ok, so the code quality looks pretty convincing to me - the new core 'undwarf' > unwinder code is a _lot_ more readable than any of the Dwarf based attempts > before. > > That we control the debug info generation at build time is icing on the cake to > me. > > One thing I'd like to see on the list of benefits side of the equation is a size > comparison of kernel .text, with frame pointers vs. undwarf, on 64-bit kernels. Ok, will do a text size comparison. The only difficulty I encountered there is that the 'size' tool considers the .undwarf section to be text for some reason. So the "text" size grew considerably :-) > Being able to generate more optimal code in the hottest code paths of the kernel > is the _real_, primary upstream kernel benefit of a different debuginfo method - > which has to be weighed against the pain of introducing a new unwinder. But this > submission does not talk about that aspect at all, which should be fixed I think. Actually I devoted an entire one-sentence paragraph to performance in the documentation: The simpler debuginfo format also enables the unwinder to be relatively fast, which is important for perf and lockdep. But I'll try to highlight that a little more. -- Josh