From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754934AbcFQAk5 (ORCPT ); Thu, 16 Jun 2016 20:40:57 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45902 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754297AbcFQAk4 (ORCPT ); Thu, 16 Jun 2016 20:40:56 -0400 X-IBM-Helo: d01dlp02.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Thu, 16 Jun 2016 17:40:51 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Thomas Gleixner , Arjan van de Ven , Eric Dumazet , Ingo Molnar , LKML , Frederic Weisbecker , Chris Mason , Arjan van de Ven , Linus Torvalds , George Spelvin Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel Reply-To: paulmck@linux.vnet.ibm.com References: <20160614204225.GI30154@twins.programming.kicks-ass.net> <20160616160215.GQ3923@linux.vnet.ibm.com> <20160616181402.GK30909@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160616181402.GK30909@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16061700-0040-0000-0000-0000009644AE X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16061700-0041-0000-0000-000004702564 Message-Id: <20160617004051.GR3923@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-16_15:,, 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=8.0.1-1604210000 definitions=main-1606170006 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 16, 2016 at 08:14:02PM +0200, Peter Zijlstra wrote: > On Thu, Jun 16, 2016 at 09:02:15AM -0700, Paul E. McKenney wrote: > > > 2) When we do that right, we can make the tick frequency a command line option > > > and just have a compiled in default. > > > > As long as there is something that tells RCU what the tick frequency > > actually is at runtime, this should not be a problem. For example, > > in rcu_implicit_dynticks_qs(), the following: > > > > rdp->rsp->jiffies_resched += 5; > > > > Would instead need to be something like: > > > > rdp->rsp->jiffies_resched += 5 * jiffies_per_tick; > > > > Changing tick frequency at runtime would be a bit more tricky, as it would > > be tough to avoid some oddball false positives during the transition. > > So the 'fun' part will be frequencies with non integer factors of 1000. > Like say HZ=300. For that we'll have to keep jiffies_remainder, and > add an extra jiffy every time that rolls over. > > That would make your case slightly more interesting than you really > want I suspect. My particular case is not that sensitive, so 1000/300 would be plenty accurate. Thanx, Paul