Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764370AbZDBSmu (ORCPT ); Thu, 2 Apr 2009 14:42:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751291AbZDBSml (ORCPT ); Thu, 2 Apr 2009 14:42:41 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:42383 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751096AbZDBSmk (ORCPT ); Thu, 2 Apr 2009 14:42:40 -0400 Subject: Re: [PATCH 5/6] perf_counter: add more context information From: Peter Zijlstra To: Ingo Molnar Cc: Paul Mackerras , Corey Ashford , linux-kernel@vger.kernel.org In-Reply-To: <20090402183417.GA843@elte.hu> References: <20090402091158.291810516@chello.nl> <20090402091319.493101305@chello.nl> <20090402113643.GF10828@elte.hu> <1238672889.8530.5908.camel@twins> <20090402181849.GD6340@elte.hu> <1238696998.5133.44.camel@laptop> <20090402183417.GA843@elte.hu> Content-Type: text/plain Date: Thu, 02 Apr 2009 20:42:35 +0200 Message-Id: <1238697755.5133.62.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1887 Lines: 51 On Thu, 2009-04-02 at 20:34 +0200, Ingo Molnar wrote: > * Peter Zijlstra wrote: > > > On Thu, 2009-04-02 at 20:18 +0200, Ingo Molnar wrote: > > > * Peter Zijlstra wrote: > > > > > > > On Thu, 2009-04-02 at 13:36 +0200, Ingo Molnar wrote: > > > > > > > > > > -#define MAX_STACK_DEPTH 255 > > > > > > +#define MAX_STACK_DEPTH 254 > > > > > > > > > > > > struct perf_callchain_entry { > > > > > > - u64 nr; > > > > > > + u32 nr, hv, kernel, user; > > > > > > u64 ip[MAX_STACK_DEPTH]; > > > > > > }; > > > > > > > > Oh, and Paul suggested using u16s right after I send it out. So > > > > I'll either send an update or send a incremental in case you > > > > already applied it. > > > > > > yes, that's probably a good idea. Although u8 might be even better - > > > do we ever want to do more than 256 deep stack vectors? Even those > > > would take quite some time to construct and pass down. > > > > We'd have to pad it with 4 more bytes to remain u64 aligned, > > ok, indeed. > > > [...] also, why restrict ourselves. That MAX_STACK_DEPTH limit is > > trivially fixable if indeed someone finds its insufficient. > > well .. think about it: walking more than 256 stack frames for every > IRQ event? Getting backtraces like: > > ... > > > does that make much sense _per event_? How do you visualize it? You can use it to calculate aggregate times. Eg. attribute the time spend in func_0 to func_1 to func_2 etc. And use a tree view based on these call-chains, allowing you to drill-down -- which is basically what the sysprof GUI does. -- 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/