Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755136AbZFHUwz (ORCPT ); Mon, 8 Jun 2009 16:52:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752072AbZFHUws (ORCPT ); Mon, 8 Jun 2009 16:52:48 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:50209 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751013AbZFHUwr (ORCPT ); Mon, 8 Jun 2009 16:52:47 -0400 Date: Mon, 8 Jun 2009 22:52:37 +0200 From: Ingo Molnar To: Hugh Dickins , Peter Zijlstra , Thomas Gleixner Cc: Arjan van de Ven , linux-kernel@vger.kernel.org Subject: Re: [PATCH] latencytop: note task_struct bloat Message-ID: <20090608205237.GA13343@elte.hu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1611 Lines: 39 * Hugh Dickins wrote: > Add belated comment to LATENCYTOP help text, making clear that this is a > much more expensive option than you might think: along with the options > it selects, it may add more than 4000 bytes to each struct task_struct > (on 64-bit; more than 2000 on 32-bit), effectively quadrupling the size > of an otherwise lean task_struct (in fact, slab on x86_64 fits only 1 > in two pages, whereas it fits 5 in two pages without LATENCYTOP=y). > > Signed-off-by: Hugh Dickins > --- > > lib/Kconfig.debug | 4 ++++ > 1 file changed, 4 insertions(+) > > --- 2.6.30-rc8/lib/Kconfig.debug 2009-05-16 10:26:16.000000000 +0100 > +++ linux/lib/Kconfig.debug 2009-06-08 18:30:50.000000000 +0100 > @@ -826,6 +826,10 @@ config LATENCYTOP > Enable this option if you want to use the LatencyTOP tool > to find out which userspace is blocking on what kernel operations. > > + Note: enabling this option may add more than 4000 bytes to each > + task_struct on a 64-bit kernel (more than 2000 bytes to task_struct > + on a 32-bit kernel), multiplying its memory usage by 4 or even 5. > + Ah, nasty - quadratics in action. This should be improved really. Arjan, what would it take to convert latencytop over to perfcounters? What would be ideal software counter for this? Ingo -- 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/