Messages in this thread | | | Subject | Re: [PATCH v3 0/3] Introduce per-task latency_nice for scheduler hints | From | Parth Shah <> | Date | Mon, 17 Feb 2020 14:27:22 +0530 |
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On 1/16/20 5:32 PM, Parth Shah wrote: > This is the 3rd revision of the patch set to introduce > latency_{nice/tolerance} 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 > > Changes in this revision are: > 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: Add new attribute latency_nice to task_struct. > - Patch 2: Clone parent task's attribute to the child task on fork > - Patch 3: Add support for sched_{set,get}attr syscall to modify > latency_nice of the task > > > The patch series can be applied on tip/sched/core at the > commit 804d402fb6f6 ("sched/rt: Make RT capacity-aware") > > > 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 (3): > 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 > > include/linux/sched.h | 1 + > include/uapi/linux/sched.h | 4 +++- > include/uapi/linux/sched/types.h | 19 +++++++++++++++++++ > kernel/sched/core.c | 21 +++++++++++++++++++++ > kernel/sched/sched.h | 18 ++++++++++++++++++ > tools/include/uapi/linux/sched.h | 4 +++- > 6 files changed, 65 insertions(+), 2 deletions(-) >
Its been a long time and few revisions since the beginning of the discussion around the latency-nice. Hence thought of asking if there is/are any further work that needs to be done for adding latency-nice attribute or am I missing any piece in here?
Thanks, Parth
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