Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753740AbcD0URY (ORCPT ); Wed, 27 Apr 2016 16:17:24 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:53414 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753682AbcD0URU (ORCPT ); Wed, 27 Apr 2016 16:17:20 -0400 X-IBM-Helo: d23dlp01.au.ibm.com X-IBM-MailFrom: hemant@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Message-ID: <57211E0C.4020205@linux.vnet.ibm.com> Date: Thu, 28 Apr 2016 01:46:12 +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: Arnaldo Carvalho de Melo CC: Masami Hiramatsu , 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> In-Reply-To: <20160427152816.GP11033@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: 16042720-0033-0000-0000-000005AB141E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3711 Lines: 99 On 04/27/2016 08:58 PM, 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. > > 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. I was talking about the "probe 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. Agreed. Makes sense. > 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 :-\ Right. -- Thanks, Hemant Kumar