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Date: Mon, 24 Feb 2020 14:29:14 +0530 From: Parth Shah <parth@...ux.ibm.com> To: linux-kernel@...r.kernel.org Cc: peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, qais.yousef@....com, chris.hyser@...cle.com, patrick.bellasi@...bug.net, valentin.schneider@....com, David.Laight@...LAB.COM, pjt@...gle.com, pavel@....cz, tj@...nel.org, dhaval.giani@...cle.com, qperret@...gle.com, tim.c.chen@...ux.intel.com Subject: [PATCH v4 0/4] Introduce per-task latency_nice for scheduler hints This is the 4th revision of the patch set to introduce latency_nice as a per task attribute. The previous version can be found at: v1: https://lkml.org/lkml/2019/11/25/151 v2: https://lkml.org/lkml/2019/12/8/10 v3: https://lkml.org/lkml/2020/1/16/319 Changes in this revision are: v3->v4: - Based on Chris's comment, added security check to refrain non-root user set lower value than the current latency_nice values. v2 -> v3: - This series changes the longer attribute name to "latency_nice" as per the comment from Dietmar Eggemann https://lkml.org/lkml/2019/12/5/394 v1 -> v2: - Addressed comments from Qais Yousef - As per suggestion from Dietmar, moved content from newly created include/linux/sched/latency_tolerance.h to kernel/sched/sched.h - Extend sched_setattr() to support latency_tolerance in tools headers UAPI Introduction: ============== This patch series introduces a new per-task attribute latency_nice to provide the scheduler hints about the latency requirements of the task [1]. Latency_nice is a ranged attribute of a task with the value ranging from [-20, 19] both inclusive which makes it align with the task nice value. The value should provide scheduler hints about the relative latency requirements of tasks, meaning the task with "latency_nice = -20" should have lower latency requirements than compared to those tasks with higher values. Similarly a task with "latency_nice = 19" can have higher latency and hence such tasks may not care much about latency. The default value is set to 0. The usecases discussed below can use this range of [-20, 19] for latency_nice for the specific purpose. This patch does not implement any use cases for such attribute so that any change in naming or range does not affect much to the other (future) patches using this. The actual use of latency_nice during task wakeup and load-balancing is yet to be coded for each of those usecases. As per my view, this defined attribute can be used in following ways for a some of the usecases: 1 Reduce search scan time for select_idle_cpu(): - Reduce search scans for finding idle CPU for a waking task with lower latency_nice values. 2 TurboSched: - Classify the tasks with higher latency_nice values as a small background task given that its historic utilization is very low, for which the scheduler can search for more number of cores to do task packing. A task with a latency_nice >= some_threshold (e.g, == 19) and util <= 12.5% can be background tasks. 3 Optimize AVX512 based workload: - Bias scheduler to not put a task having (latency_nice == -20) on a core occupying AVX512 based workload. Series Organization: ==================== - Patch 1-3: Add support for latency_nice attr in the task struct using sched_{set,get}attr syscall - Patch 4 : Add permission checks for setting the value. The patch series can be applied on tip/sched/core at the commit 000619680c37 ("sched/fair: Remove wake_cap()") References: ============ [1]. Usecases for the per-task latency-nice attribute, https://lkml.org/lkml/2019/9/30/215 [2]. Task Latency-nice, "Subhra Mazumdar", https://lkml.org/lkml/2019/8/30/829 [3]. Introduce per-task latency_tolerance for scheduler hints, https://lkml.org/lkml/2019/12/8/10 Parth Shah (4): sched: Introduce latency-nice as a per-task attribute sched/core: Propagate parent task's latency requirements to the child task sched: Allow sched_{get,set}attr to change latency_nice of the task sched/core: Add permission checks for setting the latency_nice value include/linux/sched.h | 1 + include/uapi/linux/sched.h | 4 +++- include/uapi/linux/sched/types.h | 19 +++++++++++++++++++ kernel/sched/core.c | 25 +++++++++++++++++++++++++ kernel/sched/sched.h | 18 ++++++++++++++++++ tools/include/uapi/linux/sched.h | 4 +++- 6 files changed, 69 insertions(+), 2 deletions(-) -- 2.17.2
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