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Mon, 13 Jan 2025 01:21:39 -0800 (PST) Received: from [10.125.112.6] ([103.165.80.178]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-21a9f21e279sm50133125ad.134.2025.01.13.01.21.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Jan 2025 01:21:38 -0800 (PST) Message-ID: <597384e3-6519-b10e-081b-30c3f89b6e3f@gmail.com> Date: Mon, 13 Jan 2025 17:21:32 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.0 Subject: Re: [PATCH v2] sched/core: Prioritize migrating eligible tasks in sched_balance_rq() To: mingo@redhat.com, peterz@infradead.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com Cc: linux-kernel@vger.kernel.org, Hao Jia References: <20241223091446.90208-1-jiahao.kernel@gmail.com> From: Hao Jia In-Reply-To: <20241223091446.90208-1-jiahao.kernel@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Friendly ping... On 2024/12/23 17:14, Hao Jia wrote: > From: Hao Jia > > When the PLACE_LAG scheduling feature is enabled and > dst_cfs_rq->nr_queued is greater than 1, if a task is > ineligible (lag < 0) on the source cpu runqueue, it will > also be ineligible when it is migrated to the destination > cpu runqueue. Because we will keep the original equivalent > lag of the task in place_entity(). So if the task was > ineligible before, it will still be ineligible after > migration. > > So in sched_balance_rq(), we prioritize migrating eligible > tasks, and we soft-limit ineligible tasks, allowing them > to migrate only when nr_balance_failed is non-zero to > avoid load-balancing trying very hard to balance the load. > > Below are some benchmark test results. From my test results, > this patch shows a slight improvement on hackbench. > > Benchmark > ========= > > All of the benchmarks are done inside a normal cpu cgroup in a > clean environment with cpu turbo disabled, and test machine is: > > Single NUMA machine model is 13th Gen Intel(R) Core(TM) > i7-13700, 12 Core/24 HT. > > Based on master b86545e02e8c. > > Results > ======= > > hackbench-process-pipes > vanilla patched > Amean 1 0.5837 ( 0.00%) 0.5733 ( 1.77%) > Amean 4 1.4423 ( 0.00%) 1.4503 ( -0.55%) > Amean 7 2.5147 ( 0.00%) 2.4773 ( 1.48%) > Amean 12 3.9347 ( 0.00%) 3.8880 ( 1.19%) > Amean 21 5.3943 ( 0.00%) 5.3873 ( 0.13%) > Amean 30 6.7840 ( 0.00%) 6.6660 ( 1.74%) > Amean 48 9.8313 ( 0.00%) 9.6100 ( 2.25%) > Amean 79 15.4403 ( 0.00%) 14.9580 ( 3.12%) > Amean 96 18.4970 ( 0.00%) 17.9533 ( 2.94%) > > hackbench-process-sockets > vanilla patched > Amean 1 0.6297 ( 0.00%) 0.6223 ( 1.16%) > Amean 4 2.1517 ( 0.00%) 2.0887 ( 2.93%) > Amean 7 3.6377 ( 0.00%) 3.5670 ( 1.94%) > Amean 12 6.1277 ( 0.00%) 5.9290 ( 3.24%) > Amean 21 10.0380 ( 0.00%) 9.7623 ( 2.75%) > Amean 30 14.1517 ( 0.00%) 13.7513 ( 2.83%) > Amean 48 24.7253 ( 0.00%) 24.2287 ( 2.01%) > Amean 79 43.9523 ( 0.00%) 43.2330 ( 1.64%) > Amean 96 54.5310 ( 0.00%) 53.7650 ( 1.40%) > > tbench4 Throughput > vanilla patched > Hmean 1 255.97 ( 0.00%) 275.01 ( 7.44%) > Hmean 2 511.60 ( 0.00%) 544.27 ( 6.39%) > Hmean 4 996.70 ( 0.00%) 1006.57 ( 0.99%) > Hmean 8 1646.46 ( 0.00%) 1649.15 ( 0.16%) > Hmean 16 2259.42 ( 0.00%) 2274.35 ( 0.66%) > Hmean 32 4725.48 ( 0.00%) 4735.57 ( 0.21%) > Hmean 64 4411.47 ( 0.00%) 4400.05 ( -0.26%) > Hmean 96 4284.31 ( 0.00%) 4267.39 ( -0.39%) > > Signed-off-by: Hao Jia > Suggested-by: Peter Zijlstra (Intel) > --- > Previous discussion link: https://lore.kernel.org/all/20241128084858.25220-1-jiahao.kernel@gmail.com > Link to v1: https://lore.kernel.org/all/20241218080203.80556-1-jiahao.kernel@gmail.com > > v1 to v2: > - Modify dst_cfs_rq->nr_running to dst_cfs_rq->nr_queued to > resolve conflicts with commit 736c55a02c47 ("sched/fair: > Rename cfs_rq.nr_running into nr_queued"). > > kernel/sched/fair.c | 34 ++++++++++++++++++++++++++++++++++ > 1 file changed, 34 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 5599b0c1ba9b..c884bf631e66 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9396,6 +9396,30 @@ static inline int migrate_degrades_locality(struct task_struct *p, > } > #endif > > +/* > + * Check whether the task is ineligible on the destination cpu > + * > + * When the PLACE_LAG scheduling feature is enabled and > + * dst_cfs_rq->nr_queued is greater than 1, if the task > + * is ineligible, it will also be ineligible when > + * it is migrated to the destination cpu. > + */ > +static inline int task_is_ineligible_on_dst_cpu(struct task_struct *p, int dest_cpu) > +{ > + struct cfs_rq *dst_cfs_rq; > + > +#ifdef CONFIG_FAIR_GROUP_SCHED > + dst_cfs_rq = task_group(p)->cfs_rq[dest_cpu]; > +#else > + dst_cfs_rq = &cpu_rq(dest_cpu)->cfs; > +#endif > + if (sched_feat(PLACE_LAG) && dst_cfs_rq->nr_queued && > + !entity_eligible(task_cfs_rq(p), &p->se)) > + return 1; > + > + return 0; > +} > + > /* > * can_migrate_task - may task p from runqueue rq be migrated to this_cpu? > */ > @@ -9420,6 +9444,16 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) > if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu)) > return 0; > > + /* > + * We want to prioritize the migration of eligible tasks. > + * For ineligible tasks we soft-limit them and only allow > + * them to migrate when nr_balance_failed is non-zero to > + * avoid load-balancing trying very hard to balance the load. > + */ > + if (!env->sd->nr_balance_failed && > + task_is_ineligible_on_dst_cpu(p, env->dst_cpu)) > + return 0; > + > /* Disregard percpu kthreads; they are where they need to be. */ > if (kthread_is_per_cpu(p)) > return 0;