From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933144AbcDYQ1M (ORCPT ); Mon, 25 Apr 2016 12:27:12 -0400 Received: from mail.kernel.org ([198.145.29.136]:44960 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932882AbcDYQ1K (ORCPT ); Mon, 25 Apr 2016 12:27:10 -0400 Date: Mon, 25 Apr 2016 13:27:06 -0300 From: Arnaldo Carvalho de Melo To: Alexei Starovoitov Cc: David Ahern , Arnaldo Carvalho de Melo , Peter Zijlstra , Frederic Weisbecker , Ingo Molnar , Adrian Hunter , Brendan Gregg , Alexander Shishkin , Alexei Starovoitov , He Kuang , Jiri Olsa , Masami Hiramatsu , Milian Wolff , Namhyung Kim , Stephane Eranian , Thomas Gleixner , Vince Weaver , Wang Nan , Zefan Li , Linux Kernel Mailing List Subject: Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth via sysctl Message-ID: <20160425162706.GB25218@kernel.org> References: <20160420224730.GX3677@kernel.org> <20160420230410.GA41736@ast-mbp.thefacebook.com> <20160422205232.GB7004@kernel.org> <571AA02B.90107@gmail.com> <20160422221806.GA62857@ast-mbp.thefacebook.com> <20160425161425.GA25218@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20160425161425.GA25218@kernel.org> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Mon, Apr 25, 2016 at 01:14:25PM -0300, Arnaldo Carvalho de Melo escreveu: > Em Fri, Apr 22, 2016 at 03:18:08PM -0700, Alexei Starovoitov escreveu: > > On Fri, Apr 22, 2016 at 04:05:31PM -0600, David Ahern wrote: > > > On 4/22/16 2:52 PM, Arnaldo Carvalho de Melo wrote: > > > >+int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; > > > >+ > > > >+static size_t perf_callchain_entry__sizeof(void) > > > >+{ > > > >+ return sizeof(struct perf_callchain_entry) + > > > >+ sizeof(__u64) * sysctl_perf_event_max_stack; > > > >+} > > > >+ > > > > To Alexei's comment, a max_stack of 0 still has a non-zero alloc size so > > > that should be ok. > > > > > static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]); > > > > static atomic_t nr_callchain_events; > > > > static DEFINE_MUTEX(callchain_mutex); > > > >@@ -73,7 +81,7 @@ static int alloc_callchain_buffers(void) > > > > if (!entries) > > > > return -ENOMEM; > > > > >- size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS; > > > >+ size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS; > > > > > for_each_possible_cpu(cpu) { > > > > entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL, > > > right... and looking into it further, realized that the patch is broken, > > since get_callchain_entry() is doing: > > return &entries->cpu_entries[cpu][*rctx]; > > whereas it should be dynamic offset based on sysctl_perf_event_max_stack*8 > > So definitely needs another respin. > > Huh? Can you elaborate a bit more? > > Are you saying this is a bug introduced by this patch or something > pre-existing? When we alloc we alloc: /* * Number of contexts where an event can trigger: * task, softirq, hardirq, nmi. */ #define PERF_NR_CONTEXTS 4 callchain_cpus_entries[0 .. (nr_cpu_ids - 1)][in_nmi() (3)] callchain_cpus_entries[0 .. (nr_cpu_ids - 1)][in_irq() (2)] callchain_cpus_entries[0 .. (nr_cpu_ids - 1)][in_sortirq() (1)] callchain_cpus_entries[0 .. (nr_cpu_ids - 1)][(0)] And all of these have this type: struct perf_callchain_entry { __u64 nr; __u64 ip[0]; /* /proc/sys/kernel/perf_event_max_stack */ }; So, it will return a struct_callchain_entry pointer to a 8-byte sized chunk, with just perf_callchain_entry->nr, and will not try to touch perf_callchain_entry->ip[] since sysctl_perf_event_max_stack is zero. But perf_callchain_entry->ip is not a pointer... Got it ;-\ Touché, respinning... Brendan, this probably affected you results... - Arnaldo