Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755534Ab3I3Qyd (ORCPT ); Mon, 30 Sep 2013 12:54:33 -0400 Received: from merlin.infradead.org ([205.233.59.134]:46837 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754934Ab3I3Qyc (ORCPT ); Mon, 30 Sep 2013 12:54:32 -0400 Date: Mon, 30 Sep 2013 18:54:20 +0200 From: Peter Zijlstra To: Stephane Eranian Cc: LKML , "mingo@elte.hu" , "ak@linux.intel.com" , Arnaldo Carvalho de Melo , David Ahern , Jiri Olsa , Hugh Dickins Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions Message-ID: <20130930165420.GI3081@twins.programming.kicks-ass.net> References: <20130930161546.GG3081@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1935 Lines: 39 On Mon, Sep 30, 2013 at 06:48:55PM +0200, Stephane Eranian wrote: > On Mon, Sep 30, 2013 at 6:15 PM, Peter Zijlstra wrote: > > On Mon, Sep 30, 2013 at 05:44:41PM +0200, Stephane Eranian wrote: > >> Hi, > >> > >> I was alerted by people trying to use the PERF_RECORD_MMAP2 > >> record to disambiguate virtual address mappings that there is a case > >> where the record does not contain enough information. > >> > >> As you know, the MMAP2 record adds the major, minor, ino number, > >> inode generation numbers to a mapping. But it does that only for > >> file or pseudo -file backed mappings. That covers file mmaps and also > >> SYSV shared memory segments. > >> > >> However there is a another kind of situation that arises in some > >> multi-process benchmarks where a region of memory is cloned > >> using VM_CLONE. As such, the virtual addresses match between > >> the processes but the major, minor, inode, inode generation fields > >> are all zeroes because there is no inode associated with the mapping. > >> Yet, it is important for the tool to know the mappings between the > >> processes are pointing to the same physical data. > >> > >> We need to cover this case and I am seeking for advice on how to > >> best address this need given that we discarded using the plain physical > >> address for disambiguation. > > > > Urgh.. who in his bloody mind is playing VM_CLNOE games that is not > > pthread_creatE() ? > > Some matrix multiply benchmark, I guess. So the problem is that we don't have a user visible address space identifier; with CLONE_THREAD we have the thread group id that acts like this. But for bare CLONE_VM usage there's nothing afaik. -- 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/