From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756028Ab0JKUdF (ORCPT ); Mon, 11 Oct 2010 16:33:05 -0400 Received: from www.tglx.de ([62.245.132.106]:57021 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752485Ab0JKUdE (ORCPT ); Mon, 11 Oct 2010 16:33:04 -0400 Date: Mon, 11 Oct 2010 22:32:06 +0200 (CEST) From: Thomas Gleixner To: Tim Pepper cc: LKML , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Marcio Saito , Jiri Slaby , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, John Stultz , Avantika Mathur , Peter Zijlstra , Frederic Weisbecker Subject: Re: [RFC] [PATCH] allow low HZ values? In-Reply-To: <20101011201121.GA953@tpepper-t61p.dolavim.us> Message-ID: References: <20101011201121.GA953@tpepper-t61p.dolavim.us> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 Oct 2010, Tim Pepper wrote: > I'm not necessarily wanting to open up the age old question of "what is > a good HZ", but we were doing some testing on timer tick overheads for > HPC applications and this came up... Yeah. This comes always up when the timer tick overhead on HPC is tested. And this patch is again the fundamentally wrong answer. We have told HPC folks for years that we need a kind of "NOHZ" mode for HPC where we can transparently switch off the tick when only one user space bound thread is active and switch back to normal once this thing terminates or goes into the kernel via a syscall. Sigh, nothing happened ever except for repeating the same crap patches over and over. FYI, Frederic is working on that right now. He will talk about it at the plumbers RT microconf, so you might catch him there. Thanks, tglx