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Shenoy" , Vincent Guittot , "Juri Lelli" , Dietmar Eggemann , Steven Rostedt , Ben Segall , "Mel Gorman" , Valentin Schneider , "Hillf Danton" , Shrikanth Hegde , "Jianyong Wu" , Yangyu Chen , Tingyin Duan , Vern Hao , Len Brown , Aubrey Li , Zhao Liu , Chen Yu , Libo Chen , Adam Li , Tim Chen , , Yangyu Chen , References: <5b82842ff20995cd50b422dad844664089dcd0c7.camel@linux.intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <5b82842ff20995cd50b422dad844664089dcd0c7.camel@linux.intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SGBP274CA0002.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:b0::14) 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_|PH7PR11MB6330:EE_ X-MS-Office365-Filtering-Correlation-Id: 9f50b2ff-21a4-41ea-e0a9-08de0bad0b8b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016; 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The README file can be >>> found here[2]. The score depends on how aggressive the user set the >>> /sys/kernel/debug/sched/llc_aggr_tolerance. Using the default values, >>> there is no much difference observed. While setting the >>> /sys/kernel/debug/sched/llc_aggr_tolerance to 100, 44% improvment is >>> observed. >>> >>> baseline: >>> Host time spent: 50,868ms >>> >>> sched_cache: >>> Host time spent: 28,349ms >>> >>> The time has been reduced by 44%. >> >> Milan showed no improvement across all benchmarks, which could be due to the >> CCX topology (8 CCXs × 8 CPUs) where the LLC domain is too small for this >> optimization to be effective. Moreover there could be overhead due to additional >> computations. >> >> ChaCha20-xiangshan improvement in Genoa when llc_aggr_tolerance is set to 100 seems >> due to having relatively lesser thread count. Please provide the numbers >> with default values too. Would like to know numbers on varying loads. > > I'll ask Chen Yu who did the Xiangshan experiments if he has those numbers. > Madadi, do you mean the performance score number or active thread number when llc_aggr_tolerance is set to 1(default)? The score is around with sched_cache and llc_aggr_tolerance set to 1. The active number is 128 per process, and there are 8 processes when launching the benchmark. I suppose the 128 comes from the number of online CPUs. Please let me know if you need more data. Cced Yangyu who's the author of this benchmark. ls -l /proc/14460/task/ | grep -c '^d' 128 >> >> In Power 10 and Power 11, the LLC size is 4 threads which is even smaller. Not >> expecting improvements here but will run some workloads and share the data. >> >> Not gone through the entire series yet but are the situations like say in two >> NUMA system, if a task's preferred LLC is on the wrong NUMA node for its memory, >> which takes precedence? > > We take preferred NUMA node in the consideration but we do not force task to > go to the preferred node. > > I remembered initially we limited the consideration to only LLCs in the > preferred node. But we encountered regressions in hackbench and schbench, > because when the preferred node don't have any occupancy resulting in preferred LLC > to be set to -1 (no preference), and resulted in extra task migrations. > And also the preferred node for hackbench and schbench was volatile > as they have small memory footprint. Chen Yu, please chime in if there > were other reasons you remembered. > Since the preferred NUMA node is per task, while the preferred LLC is per process, scanning only the current task's preferred node would lead to cross-node migration. This is because the process's preferred LLC may not reside within the current task's preferred node. Such a scenario could leave curr_m_a_occ at 0, and any LLC with an occupancy > 0 would then trigger a preferred LLC switch. > We'll need to revisit this part of the code to take care of such > corner case. I think ideally we should move tasks to the least loaded LLC > in the preferred node (even if no LLCs have occupancy in the preferred node), > as long as preferred NUMA node don't changes too often. > > Then we might need to introduce a new member in mm_struct to store the old occupancy, curr_m_a_occ, so that we can reliably compare the old and new occupancy - to avoid the 0 value of curr_m_a_occ. >> >> Also, what about the workloads that don't share data like stress-ng? >> The stream is single process stressing the memory without any share data, we did not observe any difference on stream. We can launch more tests on stress-ng. thanks, Chenyu> > We can test those. Ideally the controls to prevent over aggregation to preferred LLC > would keep stress-ng happy. > >> It will >> be good to make sure that most other workloads don't suffer. As mentioned, >> per process knob for llc_aggr_tolerance could help. > > Agree. We are planning to add per process knob for the next version. One thought is to use > prctl. Any other suggestions are welcome. >