From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f71.google.com (mail-pa0-f71.google.com [209.85.220.71]) by kanga.kvack.org (Postfix) with ESMTP id CF67B83102 for ; Mon, 29 Aug 2016 12:48:16 -0400 (EDT) Received: by mail-pa0-f71.google.com with SMTP id le9so276921489pab.0 for ; Mon, 29 Aug 2016 09:48:16 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id 68si39943190pfr.68.2016.08.29.09.48.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Aug 2016 09:48:16 -0700 (PDT) Date: Mon, 29 Aug 2016 18:48:09 +0200 From: Peter Zijlstra Subject: Re: [PATCH v15 04/13] task_isolation: add initial support Message-ID: <20160829164809.GW10153@twins.programming.kicks-ass.net> References: <1471382376-5443-1-git-send-email-cmetcalf@mellanox.com> <1471382376-5443-5-git-send-email-cmetcalf@mellanox.com> <20160829163352.GV10153@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Chris Metcalf Cc: Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Andrew Morton , Rik van Riel , Tejun Heo , Frederic Weisbecker , Thomas Gleixner , "Paul E. McKenney" , Christoph Lameter , Viresh Kumar , Catalin Marinas , Will Deacon , Andy Lutomirski , Michal Hocko , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Aug 29, 2016 at 12:40:32PM -0400, Chris Metcalf wrote: > On 8/29/2016 12:33 PM, Peter Zijlstra wrote: > >On Tue, Aug 16, 2016 at 05:19:27PM -0400, Chris Metcalf wrote: > >>+ /* > >>+ * Request rescheduling unless we are in full dynticks mode. > >>+ * We would eventually get pre-empted without this, and if > >>+ * there's another task waiting, it would run; but by > >>+ * explicitly requesting the reschedule, we may reduce the > >>+ * latency. We could directly call schedule() here as well, > >>+ * but since our caller is the standard place where schedule() > >>+ * is called, we defer to the caller. > >>+ * > >>+ * A more substantive approach here would be to use a struct > >>+ * completion here explicitly, and complete it when we shut > >>+ * down dynticks, but since we presumably have nothing better > >>+ * to do on this core anyway, just spinning seems plausible. > >>+ */ > >>+ if (!tick_nohz_tick_stopped()) > >>+ set_tsk_need_resched(current); > >This is broken.. and it would be really good if you don't actually need > >to do this. > > Can you elaborate? Naked use of TIF_NEED_RESCHED like this is busted. There is more state that needs to be poked to keep things consistent / working. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org