Re: [rfc patch v4.4-rt2] sched: fix up preempt lazy forward port
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2016-01-18 20:18:32
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lkml
* Mike Galbraith | 2016-01-18 10:08:23 [+0100]:
quoted hunk ↗ jump to hunk
--- 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. …
quoted hunk ↗ jump to hunk
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c@@ -3542,6 +3542,15 @@ asmlinkage __visible void __sched notracif (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