From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 3558C9000BD for ; Tue, 20 Sep 2011 16:53:32 -0400 (EDT) Received: from d06nrmr1806.portsmouth.uk.ibm.com (d06nrmr1806.portsmouth.uk.ibm.com [9.149.39.193]) by mtagate3.uk.ibm.com (8.13.1/8.13.1) with ESMTP id p8KKrK7V001646 for ; Tue, 20 Sep 2011 20:53:20 GMT Received: from d06av12.portsmouth.uk.ibm.com (d06av12.portsmouth.uk.ibm.com [9.149.37.247]) by d06nrmr1806.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p8KKrKVE2232530 for ; Tue, 20 Sep 2011 21:53:20 +0100 Received: from d06av12.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av12.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p8KKrIdP006836 for ; Tue, 20 Sep 2011 14:53:20 -0600 Date: Tue, 20 Sep 2011 21:53:17 +0100 From: Stefan Hajnoczi Subject: Re: [PATCH v5 3.1.0-rc4-tip 8/26] x86: analyze instruction and determine fixups. Message-ID: <20110920205317.GA1508@stefanha-thinkpad.localdomain> References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120127.25326.71509.sendpatchset@srdronam.in.ibm.com> <20110920171310.GC27959@stefanha-thinkpad.localdomain> <20110920181225.GA5149@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110920181225.GA5149@infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Hellwig Cc: Srikar Dronamraju , Peter Zijlstra , Ingo Molnar , Steven Rostedt , Linux-mm , Arnaldo Carvalho de Melo , Linus Torvalds , Masami Hiramatsu , Hugh Dickins , Andi Kleen , Thomas Gleixner , Jonathan Corbet , Oleg Nesterov , Andrew Morton , Jim Keniston , Roland McGrath , Ananth N Mavinakayanahalli , LKML On Tue, Sep 20, 2011 at 02:12:25PM -0400, Christoph Hellwig wrote: > On Tue, Sep 20, 2011 at 06:13:10PM +0100, Stefan Hajnoczi wrote: > > You've probably thought of this but it would be nice to skip XOL for > > nops. This would be a common case with static probes (e.g. sdt.h) where > > the probe template includes a nop where we can easily plant int $0x3. > > Do we now have sdt.h support for uprobes? That's one of the killer > features that always seemed to get postponed. Not yet but it's a question of doing roughly what SystemTap does to parse the appropriate ELF sections and then putting those probes into uprobes. Masami looked at this and found that SystemTap sdt.h currently requires an extra userspace memory store in order to activate probes. Each probe has a "semaphore" 16-bit counter which applications may test before hitting the probe itself. This is used to avoid overhead in applications that do expensive argument processing (e.g. creating strings) for probes. But this should be solvable so it would be possible to use perf-probe(1) on a std.h-enabled binary. Some distros already ship such binaries! Stefan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org