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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 9 Jul 2018 10:52:23 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w69EqMLL10813738 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 9 Jul 2018 14:52:22 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A67DAB205F; Mon, 9 Jul 2018 10:51:57 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 88B6DB2065; Mon, 9 Jul 2018 10:51:57 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 9 Jul 2018 10:51:57 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id B6F9016C1972; Mon, 9 Jul 2018 07:54:40 -0700 (PDT) Date: Mon, 9 Jul 2018 07:54:40 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: David Woodhouse , mhillenb@amazon.de, linux-kernel Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Reply-To: paulmck@linux.vnet.ibm.com References: <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> <20180709144338.GS2476@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180709144338.GS2476@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18070914-0064-0000-0000-000003275208 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009339; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01058863; UDB=6.00543385; IPR=6.00836783; MB=3.00022073; MTD=3.00000008; XFM=3.00000015; UTC=2018-07-09 14:52:24 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18070914-0065-0000-0000-000039E0196B Message-Id: <20180709145440.GR3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-09_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=634 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807090170 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 04:43:38PM +0200, Peter Zijlstra wrote: > 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 Fair points. And yes, the various asm checks and transitions have made their presence known to me in other contexts of late. :-/ So what would you suggest? Thanx, Paul