From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753288AbcHUOxA (ORCPT ); Sun, 21 Aug 2016 10:53:00 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59850 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751549AbcHUOw6 (ORCPT ); Sun, 21 Aug 2016 10:52:58 -0400 X-IBM-Helo: d03dlp01.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Sun, 21 Aug 2016 07:53:02 -0700 From: "Paul E. McKenney" To: GeHao Kang Cc: Peter Zijlstra , Chris Metcalf , =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org Subject: Re: Context switch latency in tickless isolated CPU Reply-To: paulmck@linux.vnet.ibm.com References: <86f3248c-defd-f200-9eb6-bdf420771745@mellanox.com> <20160819123437.GE10121@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16082114-0020-0000-0000-00000999AB16 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005623; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000183; SDB=6.00747670; UDB=6.00352742; IPR=6.00520295; BA=6.00004671; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012407; XFM=3.00000011; UTC=2016-08-21 14:52:56 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16082114-0021-0000-0000-000054C28CEA Message-Id: <20160821145302.GP3482@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-21_08:,, 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-1608210167 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 21, 2016 at 07:26:04PM +0800, GeHao Kang wrote: > On Fri, Aug 19, 2016 at 8:34 PM, Peter Zijlstra wrote: > > > Why are you wanting to use nohz_full if you do syscalls? > > We hope to reduce the overhead of the tick while the real time > applications run, > and these applications might do some syscalls to operate the I/O devices like > EtherCAT. If latency is all you care about, one approach is to map the device registers into userspace and do the I/O without assistance from the kernel. Alternatively, use in-memory mailbox/queuing techniques to hand the I/O off to some other thread. Thanx, Paul