From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751120AbdFAMR0 (ORCPT ); Thu, 1 Jun 2017 08:17:26 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:53505 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751054AbdFAMRZ (ORCPT ); Thu, 1 Jun 2017 08:17:25 -0400 Date: Thu, 1 Jun 2017 14:17:21 +0200 From: Peter Zijlstra To: Josh Poimboeuf Cc: Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, Linus Torvalds , Andy Lutomirski , Jiri Slaby , "H. Peter Anvin" Subject: Re: [RFC PATCH 00/10] x86: undwarf unwinder Message-ID: <20170601121721.lezoecnyah3aic6a@hirez.programming.kicks-ass.net> References: <20170601060824.wv2go3adbvx5ptmt@gmail.com> <20170601115819.3twoowcnvtrfzjzr@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170601115819.3twoowcnvtrfzjzr@treble> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 01, 2017 at 06:58:20AM -0500, Josh Poimboeuf wrote: > > 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. That's relative to a DWARF unwinder. It doesn't appear to be possible to get anywhere near a frame-pointer unwinder due to having to do this log(n) lookup for every single frame.