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dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=windriver.com; Received: from SJ0PR11MB5120.namprd11.prod.outlook.com (2603:10b6:a03:2d1::13) by BYAPR11MB3432.namprd11.prod.outlook.com (2603:10b6:a03:8a::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4264.20; Tue, 29 Jun 2021 19:15:38 +0000 Received: from SJ0PR11MB5120.namprd11.prod.outlook.com ([fe80::6df4:6859:4d:29f9]) by SJ0PR11MB5120.namprd11.prod.outlook.com ([fe80::6df4:6859:4d:29f9%6]) with mapi id 15.20.4264.026; Tue, 29 Jun 2021 19:15:38 +0000 Subject: Re: Questions related to nano_sleep()/hrtimer To: manty kuma , linux-rt-users@vger.kernel.org References: From: Chris Friesen Message-ID: Date: Tue, 29 Jun 2021 13:15:33 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [70.64.73.216] X-ClientProxiedBy: CH2PR18CA0026.namprd18.prod.outlook.com (2603:10b6:610:4f::36) To SJ0PR11MB5120.namprd11.prod.outlook.com (2603:10b6:a03:2d1::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.2.9] (70.64.73.216) by CH2PR18CA0026.namprd18.prod.outlook.com (2603:10b6:610:4f::36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4287.22 via Frontend Transport; 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I *thought* that there was code to automatically adjust the priority of the hrtimer thread based on the priority of the process it was delivering the wakeup to, but maybe I'm mis-remembering. Chris On 6/28/2021 10:54 PM, manty kuma wrote: > I went through the source code for hrtimers and understood at a decent > level about how they are working. However, I have the following > questions. > > - What is the clock source for HRTimers and what is the frequency of > this clock device? > - with timer subsystem CONFIG_HZ can go to a max of 1000 meaning at > the maximum only 1 ms latency can be reliably established. I > understand that hrtimers are not using CONFIG_HZ but i am just curious > as to what their clock source is and how 1 ns precision is achieved? > - I am using a RT kernel and I see that interrupt handlers are > executed as threaded-irqs. Is it possible to configure the priority of > the interrupt handler hrtimer_interrupt()? for a FF process, the > wakeup() is called from interrupt context(called by threaded irq) > which is actually having lesser priority than my higher priority > process. If possible I would like to change the priority of the > threaded_irq process that handles timer interrupts. I believe this > way sleep() will not take longer than expected.(I am debugging issues > where even my FF process with prio 110 sometimes fails to wake up back > in time) > > Thank you in advance! > > Regards, > Manty >