From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756889Ab0JKWrt (ORCPT ); Mon, 11 Oct 2010 18:47:49 -0400 Received: from terminus.zytor.com ([198.137.202.10]:57502 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562Ab0JKWrs (ORCPT ); Mon, 11 Oct 2010 18:47:48 -0400 Message-ID: <4CB393EB.3060405@zytor.com> Date: Mon, 11 Oct 2010 15:47:07 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Thunderbird/3.1.4 MIME-Version: 1.0 To: Thomas Gleixner CC: Benjamin Herrenschmidt , Tim Pepper , linux-kernel@vger.kernel.org, Ingo Molnar , x86@kernel.org, Marcio Saito , Jiri Slaby , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, John Stultz , Avantika Mathur Subject: Re: [RFC] [PATCH] allow low HZ values? References: <20101011201121.GA953@tpepper-t61p.dolavim.us> <1286836212.5220.19.camel@pasglop> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/11/2010 03:33 PM, Thomas Gleixner wrote: > On Tue, 12 Oct 2010, Benjamin Herrenschmidt wrote: > >> On Mon, 2010-10-11 at 13:11 -0700, 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... >> >> Note that this is also very useful when working on CPU prototypes >> implemented in FPGAs and running at something like 12Mhz :-) > > /me hands benh 0.5$ for a FPGA upgrade That's often not possible if the CPU cannot be mapped onto a single FPGA (either because the core is too large, multiple cores are tested, or because there is debugging logic is included.) The interconnects slows things down tremendously. -hpa