sched/numa: Cap PTE scanning overhead to 3% of run time
There is a fundamental mismatch between the runtime based NUMA scanning at the task level, and the wall clock time NUMA scanning at the mm level. On a severely overloaded system, with very large processes, this mismatch can cause the system to spend all of its time in change_prot_numa(). This can happen if the task spends at least two ticks in change_prot_numa(), and only gets two ticks of CPU time in the real time between two scan intervals of the mm. This patch ensures that a task never spends more than 3% of run time scanning PTEs. It does that by ensuring that in-between task_numa_work() runs, the task spends at least 32x as much time on other things than it did on task_numa_work(). This is done stochastically: if a timer tick happens, or the task gets rescheduled during task_numa_work(), we delay a future run of task_numa_work() until the task has spent at least 32x the amount of CPU time doing something else, as it spent inside task_numa_work(). The longer task_numa_work() takes, the more likely it is this happens. If task_numa_work() takes very little time, chances are low that that code will do anything, but we will not care. Reported-and-tested-by: Jan Stancek <jstancek@redhat.com> Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: mgorman@suse.de Link: http://lkml.kernel.org/r/1446756983-28173-3-git-send-email-riel@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
parent
525705d15e
commit
51170840fe
|
@ -2155,6 +2155,7 @@ void task_numa_work(struct callback_head *work)
|
||||||
unsigned long migrate, next_scan, now = jiffies;
|
unsigned long migrate, next_scan, now = jiffies;
|
||||||
struct task_struct *p = current;
|
struct task_struct *p = current;
|
||||||
struct mm_struct *mm = p->mm;
|
struct mm_struct *mm = p->mm;
|
||||||
|
u64 runtime = p->se.sum_exec_runtime;
|
||||||
struct vm_area_struct *vma;
|
struct vm_area_struct *vma;
|
||||||
unsigned long start, end;
|
unsigned long start, end;
|
||||||
unsigned long nr_pte_updates = 0;
|
unsigned long nr_pte_updates = 0;
|
||||||
|
@ -2277,6 +2278,17 @@ out:
|
||||||
else
|
else
|
||||||
reset_ptenuma_scan(p);
|
reset_ptenuma_scan(p);
|
||||||
up_read(&mm->mmap_sem);
|
up_read(&mm->mmap_sem);
|
||||||
|
|
||||||
|
/*
|
||||||
|
* Make sure tasks use at least 32x as much time to run other code
|
||||||
|
* than they used here, to limit NUMA PTE scanning overhead to 3% max.
|
||||||
|
* Usually update_task_scan_period slows down scanning enough; on an
|
||||||
|
* overloaded system we need to limit overhead on a per task basis.
|
||||||
|
*/
|
||||||
|
if (unlikely(p->se.sum_exec_runtime != runtime)) {
|
||||||
|
u64 diff = p->se.sum_exec_runtime - runtime;
|
||||||
|
p->node_stamp += 32 * diff;
|
||||||
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
/*
|
/*
|
||||||
|
|
Loading…
Reference in New Issue