Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759558Ab3IDSMe (ORCPT ); Wed, 4 Sep 2013 14:12:34 -0400 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:38558 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756930Ab3IDSMb (ORCPT ); Wed, 4 Sep 2013 14:12:31 -0400 Message-ID: <522777FF.2040906@linux.vnet.ibm.com> Date: Wed, 04 Sep 2013 23:42:15 +0530 From: Hemant User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Mark Wielaard CC: Namhyung Kim , Masami Hiramatsu , Ingo Molnar , linux-kernel@vger.kernel.org, srikar@linux.vnet.ibm.com, peterz@infradead.org, oleg@redhat.com, mingo@redhat.com, anton@redhat.com, systemtap@sourceware.org Subject: Re: [RFC PATCH 0/2] Perf support to SDT markers References: <20130903072944.4793.93584.stgit@hemant-fedora> <20130903082503.GA20732@gmail.com> <5225A937.2050507@hitachi.com> <5225E2C5.3080001@linux.vnet.ibm.com> <87a9jtt72j.fsf@sejong.aot.lge.com> <1378283148.4321.16.camel@bordewijk.wildebeest.org> In-Reply-To: <1378283148.4321.16.camel@bordewijk.wildebeest.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13090417-0260-0000-0000-000003924928 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2138 Lines: 49 On 09/04/2013 01:55 PM, Mark Wielaard wrote: > On Wed, 2013-09-04 at 15:49 +0900, Namhyung Kim wrote: >> On Tue, 03 Sep 2013 18:53:17 +0530, Hemant wrote: >>> On 09/03/2013 02:47 PM, Masami Hiramatsu wrote: >>>> Indeed, and also I'd like to know what versions of SDT this support, >>>> and where we can see the technical document of that. As far as I know, >>>> the previous(?) SDT implementation also involves ugly semaphores. >>>> Have that already gone? >> It seems it's not. I see the SDT v3 document still mentions semaphores. > It mentions them, but should normally not be used. They are there for > dtrace (source) compatibility. And you don't have to use them. > > Since normally a SDT probe marker is just a NOP it doesn't have any > overhead. But if you want to add complicated arguments that you would > normally not generate in your code, then you might want to add a > semaphore. That way you can have probes with a bit more overhead that > still have zero overhead when not being probed. > > Note that if you use the normal DTRACE_PROBE macros no semaphore will be > inserted. And you can opt to not support probes that have a semaphore in > perf if you think that is easier (just check the semaphore link-time > address for the probe, it should normally be zero). Just warn: "No way I > am going to probe something that might have a little extra overhead! I > am no debugger..." :) I agree. There will be an extra overhead but there may be some important markers (on which we need to probe) may be worth this overhead? Thanks Hemant > >>> This link shows an example of marker probing with Systemtap: >>> https://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps >> I think the link below would be more helpful for us :) >> >> http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation > Yes, that should be the canonical description. > > Cheers, > > Mark > -- 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/