From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758222Ab3EHSOr (ORCPT ); Wed, 8 May 2013 14:14:47 -0400 Received: from usmamail.tilera.com ([12.216.194.151]:45993 "EHLO USMAMAIL.TILERA.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757655Ab3EHSOp (ORCPT ); Wed, 8 May 2013 14:14:45 -0400 Message-ID: <518A9614.2010805@tilera.com> Date: Wed, 8 May 2013 14:14:44 -0400 From: Chris Metcalf User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: Linus Torvalds CC: Paul McKenney , Ingo Molnar , Linux Kernel Mailing List , Fr?d?ric Weisbecker , Peter Zijlstra , Thomas Gleixner , Andrew Morton Subject: Re: [GIT PULL, RFC] Full dynticks, CONFIG_NO_HZ_FULL feature References: <20130505110351.GA4768@gmail.com> <20130505212511.GC3659@linux.vnet.ibm.com> <20130506092537.GA8879@gmail.com> <20130506153517.GA3501@linux.vnet.ibm.com> In-Reply-To: X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/6/2013 3:32 PM, Linus Torvalds wrote: > On Mon, May 6, 2013 at 8:35 AM, Paul E. McKenney > wrote: >>> >>> I think Linus might have referred to my 'future plans' entry: > > Indeed. I feel that HPC is entirely irrelevant to anybody, > *especially* HPC benchmarks. In real life, even HPC doesn't tend to > have the nice behavior their much-touted benchmarks have. > > So as long as the NOHZ is for HPC-style loads, then quite frankly, I > don't feel it is worth it. The _only_ thing that makes it worth it is > that "future plans" part where it would actually help real loads. The work is very relevant to a lot of the actual customer applications that Tilera chips are sold into: running very low latency userspace applications that handle packet processing (or, to a lesser extent, video frame processing). For packet processing in particular, you really want to be able to guarantee that you can set up a core handling packets in userspace and get NO INTERRUPTS at all, ever. If you do get an interrupt, you end up dropping a bunch of packets on the floor. We are still using code I developed internally for this (for the curious, in my dataplane branch on kernel.org), but I expect in the relatively near future we will be trying to switch to the NOHZ stuff instead. I'm really pleased to see it start getting merged up. -- Chris Metcalf, Tilera Corp. http://www.tilera.com