Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753257AbcD0UXy (ORCPT ); Wed, 27 Apr 2016 16:23:54 -0400 Received: from e28smtp01.in.ibm.com ([125.16.236.1]:53236 "EHLO e28smtp01.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752188AbcD0UXx (ORCPT ); Wed, 27 Apr 2016 16:23:53 -0400 X-IBM-Helo: d28dlp02.in.ibm.com X-IBM-MailFrom: hemant@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Message-ID: <57211FCB.9060203@linux.vnet.ibm.com> Date: Thu, 28 Apr 2016 01:53:39 +0530 From: Hemant Kumar User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Masami Hiramatsu , Arnaldo Carvalho de Melo CC: linux-kernel@vger.kernel.org, Namhyung Kim , Peter Zijlstra , Ingo Molnar , Ananth N Mavinakayanahalli Subject: Re: [PATCH perf/core v4 14/19] perf buildid-cache: Scan and import user SDT events to probe cache References: <20160426090200.11891.43944.stgit@devbox> <20160426090422.11891.92396.stgit@devbox> <5720D86C.3010209@linux.vnet.ibm.com> <20160427152816.GP11033@kernel.org> <20160428043607.d8e89514c33f4831b564972a@kernel.org> In-Reply-To: <20160428043607.d8e89514c33f4831b564972a@kernel.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16042720-4790-0000-0000-00000F3AC738 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5315 Lines: 140 On 04/28/2016 01:06 AM, Masami Hiramatsu wrote: > On Wed, 27 Apr 2016 12:28:16 -0300 > Arnaldo Carvalho de Melo wrote: > >> Em Wed, Apr 27, 2016 at 08:49:08PM +0530, Hemant Kumar escreveu: >>> >>> On 04/26/2016 02:34 PM, Masami Hiramatsu wrote: >>>> From: Masami Hiramatsu >>>> >>>> perf buildid-cache --add scans given binary and add >>>> the SDT events to probe cache. "sdt_" prefix is appended for >>>> all SDT providers to avoid event-name clash with other pre-defined >>>> events. It is possible to use the cached SDT events as other cached >>>> events, via perf probe --add "sdt_:=". >>>> >>>> e.g. >>>> ---- >>>> # perf buildid-cache --add /lib/libc-2.17.so >>>> # perf probe --cache --list | head -n 5 >>>> /usr/lib/libc-2.17.so (a6fb821bdf53660eb2c29f778757aef294d3d392): >>>> sdt_libc:setjmp=setjmp >>>> sdt_libc:longjmp=longjmp >>>> sdt_libc:longjmp_target=longjmp_target >>>> sdt_libc:memory_heap_new=memory_heap_new >>>> # perf probe -x /usr/lib/libc-2.17.so \ >>>> -a sdt_libc:memory_heap_new=memory_heap_new >>>> Added new event: >>>> sdt_libc:memory_heap_new (on memory_heap_new >>>> in /usr/lib/libc-2.17.so) >>>> >>>> You can now use it in all perf tools, such as: >>>> >>>> perf record -e sdt_libc:memory_heap_new -aR sleep 1 >>>> >>>> # perf probe -l >>>> sdt_libc:memory_heap_new (on new_heap+183 in /usr/lib/libc-2.17.so) >>>> ---- >>> Patch looks good to me. Have a few questions below : >>> >>> What about the same binary path having different build-ids. For e.g >>> a binary say, "test" has some markers, we add it to the cache. And, >>> then the file gets rebuilt again with different build-id now. And we try >>> to add to the cache again. It shows multiple entries in the cache : >>> # perf probe --cache --list >>> /home/hemant/test (157380727e2b3854395aa915dfc91dbccc02058b): >>> sdt_user_test:marker1=marker1 >>> /home/hemant/test (64c0a018636e6d5145b09fc65839c1a4a7899f18): >>> sdt_user_test:marker1=marker1 >>> /home/hemant/test (c9e34759ae95b68fa385831041c5d9e0dd1697fb): >>> sdt_user_test:marker1=marker1 >>> ... >>> >>> But, perf list sdt shows only one entry (which it should) : >>> # perf list sdt >>> >>> List of pre-defined events (to be used in -e): >>> >>> sdt_user_test:marker1 [SDT event] >>> >>> perf probe also works as expected : >>> # perf probe -x /home/hemant/test %sdt_user_test:marker1 >>> Added new event: >>> sdt_user_test:marker1 (on %marker1 in /home/hemant/test) >>> >>> You can now use it in all perf tools, such as: >>> >>> perf record -e sdt_user_test:marker1 -aR sleep 1 >>> >>> So, the question is, do we delete the previous entries for "test" from >>> the cache once we get a newer version of "test"? >> No, we shouldn't, since those entries may be used for other tasks that >> involves using the exact DSO used for a particular perf.data session. > Agreed. And you can do it by using perf buildid-cache as below; > > # perf buildid-cache --purge /home/hemant/test > # perf buildid-cache --add /home/hemant/test > > This actually removes all old binary caches, and it maybe not > what you want. Or, you can try removing cached events too. > > # perf probe --cache -d %sdt_user_test:\* Yeah, it does work for me, but without the '%'. > # perf buildid-cache --add /home/hemant/test > >> Humm, but you are talking about what cache? The "probe cache" or the >> "build-id cache"? My previous statement was about the build-id cache. >> >> For the probe cache, humm, probably we want to keep it as well, we may >> have moved that 'test' file to some other place, renamed it, etc, but it >> continues being accessible by its content-based identifier (the >> build-id) and could be used in ways we don't envision right now. >> >> I.e. the same principle used for the build-id cache should be used for >> this probe cache, where we store things by build-id. >> >> We need to prune this from time to time and for this we have: >> >> perf buildid-cache purge >> >> But that right now is unflexible, we should have a way to ask to control >> how much is purged :-\ > Agreed, current buildid-cache --update does just rescan current > binary, but maybe it should also remove old caches. Ok. >>> [SNIP] >>>> + list_for_each_entry(note, &sdtlist, note_list) { >>>> + ret = snprintf(sdtgrp, 64, "sdt_%s", note->provider); >>>> + if (ret < 0) >>>> + break; >>>> + /* Try to find same-name entry */ >>>> + entry = probe_cache__find_by_name(pcache, sdtgrp, note->name); >>> Wouldn't it be better to compare the build-id rather than the event >>> name? So, if there is a new sdt event added to a binary, its build-id will >>> change. And, if there is no change, the build-id remains the same. > This is not such purpose, but just for folding same name SDTs(but different > addresses) on same binary. I get it. But, I was wondering whether that can be used for comparison as well. >>> Only if there is a change in the build-id, we can go for searching the >>> event name. This two level check can help optimizing the search. > That have been done in build-id.c :) Ok, probably missed it. > Thank you, > Thanks for the explanation. -- Thanks, Hemant Kumar