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Mon, 30 Sep 2024 02:22:31 +0000 Date: Mon, 30 Sep 2024 10:22:17 +0800 From: Chen Yu To: Honglei Wang CC: Oliver Sang , Ingo Molnar , "Peter Zijlstra" , Juri Lelli , "Vincent Guittot" , Dietmar Eggemann , Valentin Schneider , "Chunxin Zang" , , Chen Yu , K Prateek Nayak Subject: Re: [PATCH v2] sched/eevdf: Fix wakeup-preempt by checking cfs_rq->nr_running Message-ID: References: <20240925085440.358138-1-yu.c.chen@intel.com> <8282e4e8-6d71-4402-9eed-38865a3fc6f3@126.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8282e4e8-6d71-4402-9eed-38865a3fc6f3@126.com> X-ClientProxiedBy: MAXP287CA0024.INDP287.PROD.OUTLOOK.COM (2603:1096:a00:49::32) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|PH0PR11MB7472:EE_ X-MS-Office365-Filtering-Correlation-Id: 9bed60e0-268d-4e4d-6736-08dce0f6bcf7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7416014; 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Just > >>> not sure the purpose of the 'nr_running check' stuff. Perhaps its role is > >>> just to judge whether it’s necessary to do the preemption check. If there is > >>> at least one more ready (cfs) task in the rq and current is not eligible, we > >>> take care of the waiting tasks. Thoughts? > >> > >> I got your point and it makes sense. Whether the preemption check should be triggered > >> seems to be a heuristic trade-off to me. I'm ok with using more aggressive preemption > >> strategy as it depends on whether that workload prefers latency or throughput, and as > >> long as it did not introduce regression :-) > >> > >> Oliver, may I know if you happen to have time for a test if the following change > >> suggested by Honglei would make the regression go away? Thanks. > > > > I applied the patch directly upon 85e511df3cec, the test found it can reduce the > > regression but not totally reovered > > > > ========================================================================================= > > compiler/cpufreq_governor/ipc/iterations/kconfig/mode/nr_threads/rootfs/tbox_group/testcase: > > gcc-12/performance/socket/4/x86_64-rhel-8.3/process/50%/debian-12-x86_64-20240206.cgz/lkp-spr-r02/hackbench > > > > commit: > > 82e9d0456e06 ("sched/fair: Avoid re-setting virtual deadline on 'migrations'") > > 85e511df3cec ("sched/eevdf: Allow shorter slices to wakeup-preempt") > > 8079496d311b <--- patch from Honglei > > > > 82e9d0456e06cebe 85e511df3cec46021024176672a 8079496d311b6b0d4dae973f4df > > ---------------- --------------------------- --------------------------- > > %stddev %change %stddev %change %stddev > > \ | \ | \ > > 623219 -13.1% 541887 -3.2% 603080 hackbench.throughput > > > > Thanks a lot for running the test. The result is as expectation, as the > strategy of short slices tends to favor more frequent scheduling to help > delay-sensitive tasks acquire CPU as early as possible. > > I suspect that the current test environment does not have any special > configurations for slices. In this case, a 3.2% regression is still > somewhat significant. As Yu mentioned, this is a heuristic adjustment. > In this particular case, it seems that Yu's patch is more effective in > solving the problem. Let's delegate the preemption opportunity to the > higher-level update_curr() function. > Thanks Oliver and Hongwei. Hi Hongwei, do you mind if I added your Reviewed-by tag on this? thanks, Chenyu