Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934541Ab3IDIj0 (ORCPT ); Wed, 4 Sep 2013 04:39:26 -0400 Received: from mail4.hitachi.co.jp ([133.145.228.5]:53144 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934370Ab3IDIjX (ORCPT ); Wed, 4 Sep 2013 04:39:23 -0400 Message-ID: <5226F1B6.3000801@hitachi.com> Date: Wed, 04 Sep 2013 17:39:18 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Mark Wielaard Cc: Namhyung Kim , Hemant , 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: 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 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1952 Lines: 45 (2013/09/04 17:25), 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..." :) OK, I see. And in that case, we'd better filter out the markers which use a semaphore when list it up, since we can not enable it. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com -- 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/