leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding

Browse Source 
With various drivers wanting to inject idle time; we get people
calling idle routines outside of the idle loop proper.

Therefore we need to be extra careful about not missing
TIF_NEED_RESCHED -> PREEMPT_NEED_RESCHED propagations.

While looking at this, I also realized there's a small window in the
existing idle loop where we can miss TIF_NEED_RESCHED; when it hits
right after the tif_need_resched() test at the end of the loop but
right before the need_resched() test at the start of the loop.

So move preempt_fold_need_resched() out of the loop where we're
guaranteed to have TIF_NEED_RESCHED set.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-x9jgh45oeayzajz2mjt0y7d6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2013-11-20 12:22:37 +01:00 committed by Ingo Molnar
parent c9c8986847
commit 8cb75e0c4e
5 changed files with 42 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/mwait.h
View File

@ -53,7 +53,7 @@ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
if (!need_resched())
__mwait(eax, ecx);
}
__current_clr_polling();
current_clr_polling();
}
#endif /* _ASM_X86_MWAIT_H */

15
include/linux/preempt.h
View File

@ -134,6 +134,21 @@ do { \
#undef preempt_check_resched
#endif
#ifdef CONFIG_PREEMPT
#define preempt_set_need_resched() \
do { \
set_preempt_need_resched(); \
} while (0)
#define preempt_fold_need_resched() \
do { \
if (tif_need_resched()) \
set_preempt_need_resched(); \
} while (0)
#else
#define preempt_set_need_resched() do { } while (0)
#define preempt_fold_need_resched() do { } while (0)
#endif
#ifdef CONFIG_PREEMPT_NOTIFIERS
struct preempt_notifier;

15
include/linux/sched.h
View File

@ -2745,6 +2745,21 @@ static inline bool __must_check current_clr_polling_and_test(void)
}
#endif
static inline void current_clr_polling(void)
{
__current_clr_polling();
/*
* Ensure we check TIF_NEED_RESCHED after we clear the polling bit.
* Once the bit is cleared, we'll get IPIs with every new
* TIF_NEED_RESCHED and the IPI handler, scheduler_ipi(), will also
* fold.
*/
smp_mb(); /* paired with resched_task() */
preempt_fold_need_resched();
}
static __always_inline bool need_resched(void)
{
return unlikely(tif_need_resched());

17
kernel/cpu/idle.c
View File

@ -105,14 +105,17 @@ static void cpu_idle_loop(void)
__current_set_polling();
}
arch_cpu_idle_exit();
/*
* We need to test and propagate the TIF_NEED_RESCHED
* bit here because we might not have send the
* reschedule IPI to idle tasks.
*/
if (tif_need_resched())
set_preempt_need_resched();
}
/*
* Since we fell out of the loop above, we know
* TIF_NEED_RESCHED must be set, propagate it into
* PREEMPT_NEED_RESCHED.
*
* This is required because for polling idle loops we will
* not have had an IPI to fold the state for us.
*/
preempt_set_need_resched();
tick_nohz_idle_exit();
schedule_preempt_disabled();
}

3
kernel/sched/core.c
View File

@ -1510,8 +1510,7 @@ void scheduler_ipi(void)
* TIF_NEED_RESCHED remotely (for the first time) will also send
* this IPI.
*/
if (tif_need_resched())
set_preempt_need_resched();
preempt_fold_need_resched();
if (llist_empty(&this_rq()->wake_list)
&& !tick_nohz_full_cpu(smp_processor_id())