Date: Wed, 26 Dec 2012 20:21:54 -0800 From: Peter Wemm <peter@wemm.org> To: Alfred Perlstein <bright@mu.org> Cc: "arch@freebsd.org" <arch@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Rui Paulo <rpaulo@freebsd.org>, Alfred Perlstein <alfred@ixsystems.com> Subject: Re: UPDATE Re: making use of userland dtrace on FreeBSD Message-ID: <CAGE5yCq46NFKKzSUZq=jz0NwEnWdjPTK_0fpZ%2BwWV9FA0BSQCg@mail.gmail.com> In-Reply-To: <50DBC7E2.1070505@mu.org> References: <50D49DFF.3060803@ixsystems.com> <50DBC7E2.1070505@mu.org>
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On Wed, Dec 26, 2012 at 8:00 PM, Alfred Perlstein <bright@mu.org> wrote: > What would be the drawbacks? I don't want to hurt freebsd for heavy > performance, but I think this functionality should work out of the box for > most people. The drawbacks are mostly performance related. It defeats a certain hardware optimizations for call/return on leaf functions. It'll mostly affect things like math, crypto, compression and multimedia libraries (that's ffmpeg, bzip2/gzip/libarchive, openssl, etc) but, we generally don't seem to care about that sort of performance anyway, so what's one more loss? Of course it wouldn't be required with dwarf unwinding awareness, but we don't have that. We have -fno-omit-frame-pointer on the amd64 kernel whenever debugging is compiled in because there's no unwinder for doing stack traces. We need a dwarf2+ unwinder and somebody to instrument the call frame state through the remaining assembler code. -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com; KI6FJV "All of this is for nothing if we don't go to the stars" - JMS/B5 "If Java had true garbage collection, most programs would delete themselves upon execution." -- Robert Sewell bitcoin:188ZjyYLFJiEheQZw4UtU27e2FMLmuRBUE
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