From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.2 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URG_BIZ,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69F92C6778F for ; Mon, 9 Jul 2018 14:43:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1EFDB20849 for ; Mon, 9 Jul 2018 14:43:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="KVD1XSYI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1EFDB20849 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933045AbeGIOnz (ORCPT ); Mon, 9 Jul 2018 10:43:55 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:45088 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932508AbeGIOny (ORCPT ); Mon, 9 Jul 2018 10:43:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=aTrt4W8JyGAAEcenTVkjc3cnT5TtknK/DlTOtOV03PM=; b=KVD1XSYIHlLVpM70nfRf7Ix+1 fP9n4t/ISgv73c6iIV/AE1uxkapaey5lJJ8LFINQ1dyvTBs57ylvktHrHGtUmQoy/3+N+Pr09lytA rY1P5a69oOkQddvI+LIAdI7246dDLY7Z0H2aCFIuLrYyGmpeClXFpUg9DdhLhwL7/AnKO6xijyaYT YwnU49qXGGcpGXijqSqdxQz2CiC54mKYuIZM0F7/4rxgQ3fKBmHmUa7LJOe5GxhT3Y/ghRVwCBfaf /ePATGWfFDVMuU9qGgLHISB4k46O8rpNkbBlh8+5pxKSphEtO6XkZybGlhJIJMLQwcBIG95yB9o55 KagJQG/Bw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fcXO8-0003l9-Dm; Mon, 09 Jul 2018 14:43:40 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6DDA220297EAB; Mon, 9 Jul 2018 16:43:38 +0200 (CEST) Date: Mon, 9 Jul 2018 16:43:38 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: David Woodhouse , mhillenb@amazon.de, linux-kernel Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Message-ID: <20180709144338.GS2476@hirez.programming.kicks-ass.net> References: <20180706171150.GI3593@linux.vnet.ibm.com> <20180709085351.GC2476@hirez.programming.kicks-ass.net> <1531127935.18697.57.camel@infradead.org> <20180709104429.GI2476@hirez.programming.kicks-ass.net> <1531133801.18697.73.camel@infradead.org> <20180709110657.GL2476@hirez.programming.kicks-ass.net> <20180709123457.GM3593@linux.vnet.ibm.com> <20180709125516.GO2476@hirez.programming.kicks-ass.net> <20180709130227.GQ2512@hirez.programming.kicks-ass.net> <20180709142932.GO3593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180709142932.GO3593@linux.vnet.ibm.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 09, 2018 at 07:29:32AM -0700, Paul E. McKenney wrote: > OK, so here are our options: > > 1. Add the RCU conditional to need_resched(), as David suggests. > Peter has concerns about overhead. Not only overhead, its plain broken, because: 1) we keep preemption state in other places too 2) we check need_resched() in asm