From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752460AbdJDPOg (ORCPT ); Wed, 4 Oct 2017 11:14:36 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:43916 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752343AbdJDPOf (ORCPT ); Wed, 4 Oct 2017 11:14:35 -0400 Date: Wed, 4 Oct 2017 08:14:31 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Steven Rostedt , pmladek@suse.com, sergey.senozhatsky@gmail.com, linux-kernel@vger.kernel.org, mingo@kernel.org, tglx@linutronix.de Subject: Re: [PATCH 3/3] early_printk: Add simple serialization to early_vprintk() Reply-To: paulmck@linux.vnet.ibm.com References: <20170928121823.430053219@infradead.org> <20170928122513.431444176@infradead.org> <20171003182422.025d0a67@gandalf.local.home> <20171004090830.p5kwzu6ex2wimh4v@hirez.programming.kicks-ass.net> <20171004090401.3a5123a6@gandalf.local.home> <20171004141745.GH3521@linux.vnet.ibm.com> <20171004104354.2ecb23e9@gandalf.local.home> <20171004145247.4tp6r6ds6e5pkut5@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171004145247.4tp6r6ds6e5pkut5@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17100415-0040-0000-0000-000003ACADC3 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007842; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000233; SDB=6.00926408; UDB=6.00466026; IPR=6.00706620; BA=6.00005620; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017391; XFM=3.00000015; UTC=2017-10-04 15:14:33 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17100415-0041-0000-0000-000007A1BE01 Message-Id: <20171004151431.GI3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-04_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710040213 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 04, 2017 at 04:52:47PM +0200, Peter Zijlstra wrote: > On Wed, Oct 04, 2017 at 10:43:54AM -0400, Steven Rostedt wrote: > > > > My question is not about ordering, but about coherency. Can you have > > one CPU read a variable that goes into cache, and keep using the cached > > variable every time the program asks to read it, instead of going out > > to memory. > > No, not on a coherent system. What Peter said. And if you use READ_ONCE() for the reads, than as far as I know, all the systems that the Linux kernel supports are coherent systems. Thanx, Paul