From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: [PATCH] sched/rt: don't try to balance rt_runtime when it is futile Date: Thu, 27 Nov 2014 17:17:38 +0800 Message-ID: <5476EC32.9030005@gmail.com> References: <1400080115-12339-1-git-send-email-paul.gortmaker@windriver.com> <20140514154459.GE4570@linux.vnet.ibm.com> <20140514191100.GA24155@windriver.com> <1400122194.5175.18.camel@marge.simpson.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Ingo Molnar , Frederic Weisbecker , Peter Zijlstra , Steven Rostedt , Thomas Gleixner To: Mike Galbraith , Paul Gortmaker Return-path: Received: from mail-pd0-f171.google.com ([209.85.192.171]:34351 "EHLO mail-pd0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932114AbaK0JR5 (ORCPT ); Thu, 27 Nov 2014 04:17:57 -0500 In-Reply-To: <1400122194.5175.18.camel@marge.simpson.net> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Hi Mike, On 5/15/14, 10:49 AM, Mike Galbraith wrote: > On Wed, 2014-05-14 at 15:11 -0400, Paul Gortmaker wrote: > >> Given that, perhaps a separate change to sched_rt_runtime_exceeded() >> that works out the CPU from the rt_rq, and returns zero if it is a >> nohz_full cpu? Does that make sense? Then the nohz_full people won't >> get the throttling message even if they go 100%. > I don't get it. What reason would there be to run a hog on a dedicated > core as realtime policy/priority? Given no competition, there's nothing > to prioritize, you could just as well run a critical task as SCHED_IDLE. > > I would also expect that anyone wanting bare metal will have all of > their critical cores isolated from the scheduler, watchdogs turned off > as well as that noisy throttle, the whole point being to make as much > silent as possible. Seems to me tick_nohz_full_cpu(cpu) should be > predicated by that cpu being isolated from the #1 noise source, the > scheduler and its load balancing. There's just no point to nohz_full > without that, or if there is, I sure don't see it. If the tick is still need to be handled if cpu is isolated w/o nohz full enabled? Regards, Wanpeng Li > > When I see people trying to run a hog as a realtime task, it's because > they are trying in vain to keep competition away from precious cores.. > and one mlockall with a realtime hog blocking flush_work() gives them a > wakeup call. > > -Mike > > -- > 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/