Messages in this thread Patch in this message | | | Date | Tue, 18 Feb 2020 17:47:19 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH 3/3] sched/rt: fix pushing unfit tasks to a better CPU |
| |
On 02/18/20 09:46, Pavan Kondeti wrote: > The original RT task placement i.e without capacity awareness, places the task > on the previous CPU if the task can preempt the running task. I interpreted it > as that "higher prio RT" task should get better treatment even if it results > in stopping the lower prio RT execution and migrating it to another CPU. > > Now coming to your patch (merged), we force find_lowest_rq() if the previous > CPU can't fit the task though this task can right away run there. When the > lowest mask returns an unfit CPU (with your new patch), We have two choices, > either to place it on this unfit CPU (may involve migration) or place it on > the previous CPU to avoid the migration. We are selecting the first approach. > > The task_cpu(p) check in find_lowest_rq() only works when the previous CPU > does not have a RT task. If it is running a lower prio RT task than the > waking task, the lowest_mask may not contain the previous CPU. > > I don't if any workload hurts due to this change in behavior. So not sure > if we have to restore the original behavior. Something like below will do.
Is this patch equivalent to yours? If yes, then I got you. If not, then I need to re-read this again..
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index ace9acf9d63c..854a0c9a7be6 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1476,6 +1476,13 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) if (test || !rt_task_fits_capacity(p, cpu)) { int target = find_lowest_rq(p);
+ /* + * Bail out if we were forcing a migration to find a better + * fitting CPU but our search failed. + */ + if (!test && !rt_task_fits_capacity(p, target)) + goto out_unlock; + /* * Don't bother moving it if the destination CPU is * not running a lower priority task. @@ -1484,6 +1491,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) p->prio < cpu_rq(target)->rt.highest_prio.curr) cpu = target; } + +out_unlock: rcu_read_unlock();
out:
> > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index 4043abe..c80d948 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -1475,11 +1475,15 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags) > int target = find_lowest_rq(p); > > /* > - * Don't bother moving it if the destination CPU is > - * not running a lower priority task. > + * Don't bother moving it > + * > + * - If the destination CPU is not running a lower priority task > + * - The task can't fit on the destination CPU and it can run > + * right away on it's previous CPU. > */ > - if (target != -1 && > - p->prio < cpu_rq(target)->rt.highest_prio.curr) > + if (target != -1 && target != cpu && > + p->prio < cpu_rq(target)->rt.highest_prio.curr && > + (test || rt_task_fits_capacity(p, target))) > cpu = target; > } > rcu_read_unlock(); > > Thanks, > Pavan > > -- > Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
| |