From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752667AbbJTVSi (ORCPT ); Tue, 20 Oct 2015 17:18:38 -0400 Received: from mail-db3on0095.outbound.protection.outlook.com ([157.55.234.95]:13568 "EHLO emea01-db3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751592AbbJTVSf (ORCPT ); Tue, 20 Oct 2015 17:18:35 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=cmetcalf@ezchip.com; Subject: Re: [PATCH v8 08/14] nohz_full: allow disabling the 1Hz minimum tick at boot To: Frederic Weisbecker References: <1445373372-6567-1-git-send-email-cmetcalf@ezchip.com> <1445373372-6567-9-git-send-email-cmetcalf@ezchip.com> <20151020210331.GC29289@lerouge> CC: Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Peter Zijlstra , Andrew Morton , Rik van Riel , Tejun Heo , Thomas Gleixner , "Paul E. McKenney" , Christoph Lameter , Viresh Kumar , Catalin Marinas , Will Deacon , Andy Lutomirski , , From: Chris Metcalf Message-ID: <5626AF95.8090805@ezchip.com> Date: Tue, 20 Oct 2015 17:18:13 -0400 User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151020210331.GC29289@lerouge> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [12.216.194.146] X-ClientProxiedBy: CY1PR1201CA0005.namprd12.prod.outlook.com (25.169.17.143) To HE1PR02MB0778.eurprd02.prod.outlook.com (25.161.118.142) X-Microsoft-Exchange-Diagnostics: 1;HE1PR02MB0778;2:kyxXLAAZkvtbaUFL/1QyIQJoj+u8iAAVnaB8BCqjaEdLxCvFPeYN+/vMDO1DChuG4NmkM1qXiycQGXgTDKLckc9mOcnX4iR/fIuJeOB/kNn1dPdYsypmupIkvm3acP0UITO/BirzNcvTvPNIXwoNMH2cUePdsWYuvx+gmpECouU=;3:ufZERLgsW4Rgc9LQaXsOfFQe45YVCs1x72ySkxIgA3bQwxkukqWXEcc8r2wJakqiiG+k06KcXdpdOEKPaSbf/mjQ3wEmOlps9l6fHeYyhjjwTZHvDA3M3+9Fz0gYPJ+dxZIeluF3EReYU03NvH2stw==;25:kHZ8xSJOUB7ppO8ys/zBS9/CZR9Ll5GdAZo+IebzFX3QQqZaQ4e0Zq41kKqRpDC7TDB03MVzVbIurT01c+ESiK7RHWnGw9X5Ie6XcGEbOpPm3B4zh9k8bI0MbDmaEDeYkXmn+whC6piMgnv/ufZk3xmZytJv3GyJ3SsIUKNVpDYRR7OC/9RzlgdIoVbgkd/2VZCSFH6MXdbndGetmg/6YzMhQuvJyCJboqh5Se2vtHv8hGM1SBVk1kJ3ZViAgSdKsUqUwrMBd/zMp3XC2MjLJA==;20:mjH2/HdbDiNfDQDdme3dnJq42wIz0gbHuLa0aUWAqQWFDeFckyQDdlN8TGeW+nri10EiaVqDKWtPTiN45DA0G5Pups2ZG2IrW+fUjhCalIAbpu+vP5L6byMIpFlV5OdudqdMb30L3mlPIMzYeoql6PREhYZ23MheiErDBnyZXN4= X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:HE1PR02MB0778; X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:(121898900299872); X-Exchange-Antispam-Report-CFA-Test: BCL:0;PCL:0;RULEID:(601004)(2401047)(5005006)(520078)(8121501046)(3002001);SRVR:HE1PR02MB0778;BCL:0;PCL:0;RULEID:;SRVR:HE1PR02MB0778; X-Microsoft-Exchange-Diagnostics: 1;HE1PR02MB0778;4:1SVB19YET86IzSMm5Lov3BslEKReGiCXZ5E69PfQpLlCg1m6QNyaEoIinrJdhXp9Fiw+R4rvPOQFxb7W3rnPzXReX4lp3MydUjsYrdjWQnA/SpZ3CA0Brl7FRUITqf+TFH77CwZnIizggATG6FS87k5UCQ6yZM7qXEncQSXPdas4/0C565jc7rkOSYR3W2/zzR35M/lzb3nIbRhZA9tqDIx4AED+2uKrVMzsRtJikNf2ylOhiL/busnZHM0keSezFTBsNWf6NAnyNgQ89FP406yxlcdRBd68QtI/cotFPdcTX76RXJp+qrGyJp5zZDO8IPerqDjFSo1nCFkHP72FEZHTJPCPfBbIwgLsmxvdRlw= X-Forefront-PRVS: 073515755F X-Forefront-Antispam-Report: SFV:NSPM;SFS:(10009020)(6009001)(6049001)(24454002)(479174004)(377454003)(189002)(199003)(59896002)(50986999)(23746002)(106356001)(80316001)(86362001)(19580405001)(50466002)(19580395003)(76176999)(122386002)(105586002)(101416001)(5004730100002)(46102003)(87266999)(54356999)(65816999)(5008740100001)(40100003)(81156007)(47776003)(189998001)(110136002)(5007970100001)(33656002)(77096005)(4001350100001)(561944003)(65806001)(5001960100002)(15975445007)(92566002)(97736004)(64126003)(64706001)(2950100001)(83506001)(36756003)(65956001)(1411001)(87976001)(66066001)(42186005)(18886065003);DIR:OUT;SFP:1101;SCL:1;SRVR:HE1PR02MB0778;H:[10.7.0.41];FPR:;SPF:None;PTR:InfoNoRecords;MX:1;A:1;LANG:en; X-Microsoft-Exchange-Diagnostics: =?Windows-1252?Q?1;HE1PR02MB0778;23:5hXoOJLzFFz6zQ3R34T1RcBUwpSk19pvB22CW?= =?Windows-1252?Q?FaS/qtag1x/acmsZ2j5Gw+oNYwGKD1s7dgL2P7ZPc2Drfz1cyS1tsZ+Z?= =?Windows-1252?Q?yANxDfy6QN3Okpsp+EkrcOW/CRKbP1tOmA4xuxKDww5+AZlSHee0v90g?= =?Windows-1252?Q?o1uX8EGUl6DN3WCZZWMhjSmXU2jVRcv1mtuot52uJGTir427ZGRtafC6?= =?Windows-1252?Q?o2ub7MiQ2/4M7foVRRQSYSXedwu4xh0AAUAd7/ekHP58p5jXUOgjxOzk?= =?Windows-1252?Q?H2d2cgkf8Hn5Fgu7HbKSzColOUbxsD+KpL4inBq1loJRxwgTPD8NIWe4?= =?Windows-1252?Q?qisVJTa+tas4oNKCs0l+e9WqlLGRAWJNCfrCUURGzdewQlQpFo46tQex?= =?Windows-1252?Q?HHGJTuV4YCq2B3qiSoy/vyTqAmH6bJTVqDBDoXE0CKR36KGp2ml/qIRA?= =?Windows-1252?Q?ffSJiUW8wN2SkDtsZEu/X+h/clTg0l4f93rPSh5BM3JvmFa87N+jscbe?= =?Windows-1252?Q?yQZMEAuYJbBEx8I7k4dz0xo0Pqs76xaNle2ZEGPUMxMWNaatin6B2ZGv?= =?Windows-1252?Q?VXWDzRBACE7xbTSeljal9qOr/NtIvfeRhDwu/n0U88YbRWXVRWh3S80R?= =?Windows-1252?Q?TLt8oTgq8RUO99qfKeCRoW5T03Ij1BPA55my3ncpLHntMDUsWW07pOCH?= =?Windows-1252?Q?djzogta4zwpEwUd/TCTZ9aNMH+DVXplaDM4OeimEeVBztv2Ic0+y/62u?= =?Windows-1252?Q?vki5vRIqpa7B4YO71XjfqqnsMzvWlAef1Y9HuzDGtrXs0u9jqWYkiIVy?= =?Windows-1252?Q?9QyzVvRWC/GpUj4l2+NUvmAdLCD5LMjBjA7ZAKpaljwvJVNqM1Bmxk7U?= =?Windows-1252?Q?eiAw0YHDq3rnJ9DnENkSZB9tB4GVQ/9UKnLNaO0u2yWOSFiGYL5V9ut/?= =?Windows-1252?Q?ohfLEB7HzePguMHNVtWYaZLD5US0UoI/B3NyDYpI01HwUvQSnynLCSSM?= =?Windows-1252?Q?oGr/dLxdk9tGphK5dRu8QcvD9o5u+FGnwBkK7Go3a7n81/9F6TtU52Do?= =?Windows-1252?Q?ocsLWh8oWSRha9ElUVV/LuteDNazTBl2IQcM72C8i0fBIlPV69TD31ys?= =?Windows-1252?Q?6DmjwyEiRq8BcprbBdbfBPEX+l91UOlzQrzXy4jiZ2zQAB0XjVY4f6qr?= =?Windows-1252?Q?aNqf3M/vrCaZoTduWiraYXK++Tzr10Xr0AJ7lbCT6kfxoaPIehERmznb?= =?Windows-1252?Q?VvkEL27L7DN4FPQNAyyLapvHEF05kmOFDywqehCCckheXB70x8iE5052?= =?Windows-1252?Q?eeVPeksLhVVSy9X78w+by99OTM++5aUW4+XCzhbDfLXweTlDiHR0vpLu?= =?Windows-1252?Q?YE/okCB/gLoW+OlpUKRY+ldJZFpqYwvImko8PHOH8bIzqMxE9EW7xdmz?= =?Windows-1252?Q?+SzjinhTSuWtaxcsFG9VS03C1JdF1+4J7jCrt+62g=3D=3D?= X-Microsoft-Exchange-Diagnostics: 1;HE1PR02MB0778;5:TvstM3AvTtqwMFdT0ottJgfjtCeJ2SI1Qh5t37gaRiqJoxWARKDerEh8tQG2eg0yQ0KvMgGMUoGc9UZrc6fJOGbAQvjVlcYdKgTpGb+8DV0ASVO28Jpp6LD30T3vXiOJs0fYZ7uYdvR+xOLAZKvDCQ==;24:DNRa3NGWCz4NEppO/dOKVOreVdcTIelMqoOikuTBfrBm7iqOmY+me9X9x6E+jjEEmbOaAks4CJbq+buZJ0bJU2yh6seQpfgMHPX3TzbVe3I=;20:KRzFhQSZFp9VOyHOnNT7gNKGj6gZPpIhPMTBZnag6awwr9Fvi/a+oiC3d1ZZk8IqtmD4m5qmh18dAfoWyqkCPQ== SpamDiagnosticOutput: 1:23 SpamDiagnosticMetadata: NSPM X-OriginatorOrg: ezchip.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Oct 2015 21:18:26.7762 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR02MB0778 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/20/2015 05:03 PM, Frederic Weisbecker wrote: > On Tue, Oct 20, 2015 at 04:36:06PM -0400, Chris Metcalf wrote: >> While the current fallback to 1-second tick is still required for >> a number of kernel accounting tasks (e.g. vruntime, load balancing >> data, and load accounting), it's useful to be able to disable it >> for testing purposes. Paul McKenney observed that if we provide >> a mode where the 1Hz fallback timer is removed, this will provide >> an environment where new code that relies on that tick will get >> punished, and we won't forgive such assumptions silently. >> >> This option also allows easy testing of nohz_full and task-isolation >> modes to determine what functionality needs to be implemented, >> and what possibly-spurious timer interrupts are scheduled when >> the basic 1Hz tick has been turned off. >> >> Signed-off-by: Chris Metcalf > There have been proposals to disable/tune the 1 Hz tick via debugfs which > I Nacked because once you give such an opportunity to the users, they > will use that hack and never fix the real underlying issue. > > For the same reasons, I'm sorry but I have to Nack this proposal as well. > > If this is for development or testing purpose, scheduler_max_tick_deferment() is > easily commented out. Fair enough and certainly your prerogative, so don't hesitate to say "no" to the following argument. :-) I would tend to differentiate a debugfs proposal from a boot flag proposal: a boot flag is a more hardcore thing to change, and it's not like application developers will come along and explain that you have to boot with different flags to run their app - whereas if they can just sneak in a modification to a debugfs setting that's much easier for the app to tweak. So perhaps a boot flag is an acceptable compromise between "nothing" and a debugfs tweak? It certainly does make it easier to hack on the task-isolation code, and likely other things where people are trying out fixes to subsystems where they are attempting to remove the reliance on the tick. -- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com