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Wed, 3 Jun 2026 13:26:53 +0000 Message-ID: <8b5ee890-8245-4bde-af41-c689e3e12792@intel.com> Date: Wed, 3 Jun 2026 15:26:47 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] rtase: Avoid sleeping in get_stats64() To: David Laight CC: Justin Lai , , , , , , , , , , References: <20260601062447.64027-1-justinlai0215@realtek.com> <20260601224203.5d282c21@pumpkin> <20260603105929.5f278675@pumpkin> Content-Language: en-US From: Alexander Lobakin In-Reply-To: <20260603105929.5f278675@pumpkin> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: VI1P190CA0010.EURP190.PROD.OUTLOOK.COM (2603:10a6:802:2b::23) To DS0PR11MB8718.namprd11.prod.outlook.com (2603:10b6:8:1b9::20) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB8718:EE_|DS7PR11MB6174:EE_ X-MS-Office365-Filtering-Correlation-Id: 45ac5f86-69cd-4cd3-4db8-08dec173c6c0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|56012099006|4143699003|11063799006|22082099003|6133799003|18002099003; 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This may >>>>> sleep while waiting for the hardware counter dump to complete. >>>>> >>>>> Use read_poll_timeout_atomic() instead to avoid sleeping in the >>>>> get_stats64() path. >>>>> >>>>> Signed-off-by: Justin Lai >>>> >>>> Looks legit. >>>> >>>> One question: for how long can this poll for in real life scenarios? Up >>>> to ~1 ms is okay-ish for atomic, but if longer, then you'd better to >>>> split it into shorter polls and reschedule() time to time. >>> >>> Anyone trying to get a thread running at an RT priority won't thank you >>> for spinning for anywhere near that long. >>> When an RT processes becomes runnable the scheduler will preempt a lower >>> priority process that is running on the cpu the RT process last ran on. >>> The RT process won't run until the preempt actually happens. >>> >>> 1ms is a very long time. >> >> That's why I wrote "okay-ish". Ideally atomic polling should not go past >> 100 us, I usually used it for no longer than 10-50 us. >> >> The author says that it usually takes around 25 us which is acceptable >> I'd say. > > Just about :-) > > Would anyone notice if the read stats code returned slightly old values > and did a async request to get the current ones? Yep, async would be ideal here. > > Probably more work for a back-port though. > > -- David Thanks, Olek