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SubjectRe: [rfc patch v4.4-rt2] sched: fix up preempt lazy forward port
* Mike Galbraith | 2016-01-18 10:08:23 [+0100]:

>--- a/arch/x86/entry/common.c
>+++ b/arch/x86/entry/common.c
>@@ -220,14 +220,14 @@ long syscall_trace_enter(struct pt_regs
>
> #define EXIT_TO_USERMODE_LOOP_FLAGS \
> (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
>- _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
>+ _TIF_NEED_RESCHED_MASK | _TIF_USER_RETURN_NOTIFY)
>

If I read this right, the loop where this define is used
_TIF_ALLWORK_MASK in v4.1 of which _TIF_NEED_RESCHED_MASK was part of.
Adding this will reassmeble the old behaviour.


>--- a/kernel/sched/core.c
>+++ b/kernel/sched/core.c
>@@ -3542,6 +3542,15 @@ asmlinkage __visible void __sched notrac
> if (likely(!preemptible()))
> return;
>
>+#ifdef CONFIG_PREEMPT_LAZY
>+ /*
>+ * Check for lazy preemption
>+ */
>+ if (current_thread_info()->preempt_lazy_count &&
>+ !test_thread_flag(TIF_NEED_RESCHED))
>+ return;
>+#endif
>+

And this is a new piece. So you forbid that tasks leave the CPU if
lazy_count > 0. Let me look closed why this is happening and if this is
v4.1 … v4.4 or not.

> preempt_schedule_common();
> }
> NOKPROBE_SYMBOL(preempt_schedule);

Sebastian

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