Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754456Ab0ARWQP (ORCPT ); Mon, 18 Jan 2010 17:16:15 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752613Ab0ARWQP (ORCPT ); Mon, 18 Jan 2010 17:16:15 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:47694 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751947Ab0ARWQO (ORCPT ); Mon, 18 Jan 2010 17:16:14 -0500 Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP) From: Jim Keniston To: Pekka Enberg Cc: Avi Kivity , 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 In-Reply-To: <4B545ACF.40203@cs.helsinki.fi> 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> Content-Type: text/plain Date: Mon, 18 Jan 2010 14:15:57 -0800 Message-Id: <1263852957.2266.38.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.12.3 (2.12.3-8.el5_2.3) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1678 Lines: 41 On Mon, 2010-01-18 at 14:57 +0200, Pekka Enberg wrote: > On 01/18/2010 02:51 PM, Pekka Enberg wrote: > >> And how many probes do we expected to be live at the same time in > >> real-world scenarios? I guess Avi's "one million" is more than enough? > > Avi Kivity kirjoitti: > > I don't think a user will ever come close to a million, but we can > > expect some inflation from inlined functions (I don't know if uprobes > > replicates such probes, but if it doesn't, it should). > > Right. I guess we're looking at few megabytes of the address space for > normal scenarios which doesn't seem too excessive. > > However, as Peter pointed out, the bigger problem is that now we're > opening the door for other features to steal chunks of the address > space. And I think it's a legitimate worry that it's going to cause > problems for 32-bit in the future. > > I don't like the idea but if the performance benefits are real (are > they?), Based on what seems to be the closest thing to an apples-to-apples comparison -- counting the number of calls to a specified function -- uprobes is 6-7 times faster than the ptrace-based equivalent, ltrace -c. And of course, uprobes provides much, much more flexibility, appears to scale better, and works with multithreaded apps. Likewise, FWIW, utrace is more than 10x faster than strace -c in counting system calls. > maybe it's a worthwhile trade-off. Dunno. > > Pekka Jim -- 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/