Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752551Ab0ATJoI (ORCPT ); Wed, 20 Jan 2010 04:44:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752521Ab0ATJoG (ORCPT ); Wed, 20 Jan 2010 04:44:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45592 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202Ab0ATJoF (ORCPT ); Wed, 20 Jan 2010 04:44:05 -0500 Message-ID: <4B56D027.3010808@redhat.com> Date: Wed, 20 Jan 2010 11:43:03 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091209 Fedora/3.0-4.fc12 Thunderbird/3.0 MIME-Version: 1.0 To: Jim Keniston CC: Pekka Enberg , Srikar Dronamraju , Peter Zijlstra , ananth@in.ibm.com, Ingo Molnar , Arnaldo Carvalho de Melo , utrace-devel , Frederic Weisbecker , Masami Hiramatsu , Maneesh Soni , Mark Wielaard , LKML Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) References: <1263740593.557.20967.camel@twins> <1263800752.4283.19.camel@laptop> <4B543F93.3060509@redhat.com> <1263815072.4283.305.camel@laptop> <4B544D7C.2060708@redhat.com> <1263816396.4283.361.camel@laptop> <4B544F8E.1080603@redhat.com> <84144f021001180413w76a8ca2axb0b9f07ee4dea67e@mail.gmail.com> <4B545146.3080001@redhat.com> <20100118124419.GC1628@linux.vnet.ibm.com> <84144f021001180451k2a84f17x3dc24796fea986c9@mail.gmail.com> <4B5459CA.9060603@redhat.com> <4B545ACF.40203@cs.helsinki.fi> <1263852957.2266.38.camel@localhost.localdomain> <4B556855.6040800@redhat.com> <1263923265.4998.28.camel@localhost.localdomain> In-Reply-To: <1263923265.4998.28.camel@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1575 Lines: 42 On 01/19/2010 07:47 PM, Jim Keniston wrote: > >> This is still with a kernel entry, yes? >> > Yes, this involves setting a breakpoint and trapping into the kernel > when it's hit. The 6-7x figure is with the current 2-trap approach > (breakpoint, single-step). Boosting could presumably make that more > like 12-14x. > A trap is IIRC ~1000 cycles, we can reduce this to ~50 (totally negligible from the executed code's point of view). >> Do you have plans for a variant >> that's completely in userspace? >> > I don't know of any such plans, but I'd be interested to read more of > your thoughts here. As I understand it, you've suggested replacing the > probed instruction with a jump into an instrumentation vma (the XOL > area, or something similar). Masami has demonstrated -- through his > djprobes enhancement to kprobes -- that this can be done for many x86 > instructions. > > What does the code in the jumped-to vma do? 1. Write a trace entry into shared memory, trap into the kernel on overflow. 2. Trap if a condition is satisfied (fast watchpoint implementation). > Is the instrumentation code > that corresponds to the uprobe handlers encoded in an ad hoc .so? > Looks like a good idea, but it doesn't matter much to me. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/