Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753284Ab0ARRLN (ORCPT ); Mon, 18 Jan 2010 12:11:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753130Ab0ARRLM (ORCPT ); Mon, 18 Jan 2010 12:11:12 -0500 Received: from e31.co.us.ibm.com ([32.97.110.149]:45014 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752203Ab0ARRLJ (ORCPT ); Mon, 18 Jan 2010 12:11:09 -0500 Date: Mon, 18 Jan 2010 22:40:38 +0530 From: Ananth N Mavinakayanahalli To: Avi Kivity Cc: Pekka Enberg , Peter Zijlstra , Jim Keniston , Srikar Dronamraju , 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) Message-ID: <20100118171038.GB4424@in.ibm.com> Reply-To: ananth@in.ibm.com References: <4B53661A.9090907@redhat.com> <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> <20100118154323.GA4424@in.ibm.com> <4B5491D0.20501@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B5491D0.20501@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1333 Lines: 30 On Mon, Jan 18, 2010 at 06:52:32PM +0200, Avi Kivity wrote: > On 01/18/2010 05:43 PM, Ananth N Mavinakayanahalli wrote: >>> >>>> Well, the alternatives are very unappealing. Emulation and single-stepping >>>> are going to be very slow compared to a couple of jumps. >>>> >>> So how big chunks of the address space are we talking here for uprobes? >>> >> As Srikar mentioned, the least we start with is 1 page. Though you can >> have as many probes as you want, there are certain optimizations we can >> do, depending on the most common usecases. >> >> For eg., if you'd consider the start of a routine to be the most >> commonly traced location, most routines in a binary would generally >> start with the same instruction (say push %ebp), and we can refcount a >> slot with that instruction to be used for all probes of the same >> instruction. >> > > But then you can't follow the instruction with a jump back to the code... Right. This will work only for the non boosted case where single-stepping is mandatory. I guess the tradeoff is vma space and speed. Ananth -- 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/