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sched: Add TIF_NEED_RESCHED_LAZY infrastructure

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Add the basic infrastructure to split the TIF_NEED_RESCHED bit in two.
Either bit will cause a resched on return-to-user, but only
TIF_NEED_RESCHED will drive IRQ preemption.

No behavioural change intended.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lkml.kernel.org/r/20241007075055.219540785@infradead.org
This commit is contained in:
Peter Zijlstra 2024-10-04 14:47:02 +02:00
parent 0f0d1b8e50
commit 26baa1f1c4
7 changed files with 48 additions and 24 deletions
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3
include/linux/entry-common.h
View File

@ -64,7 +64,8 @@
#define EXIT_TO_USER_MODE_WORK \
(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
_TIF_NEED_RESCHED | _TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | \
_TIF_PATCH_PENDING | _TIF_NOTIFY_SIGNAL | \
ARCH_EXIT_TO_USER_MODE_WORK)
/**

5
include/linux/entry-kvm.h
View File

@ -17,8 +17,9 @@
#endif
#define XFER_TO_GUEST_MODE_WORK \
(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \
_TIF_NOTIFY_RESUME | ARCH_XFER_TO_GUEST_MODE_WORK)
(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | _TIF_SIGPENDING | \
_TIF_NOTIFY_SIGNAL | _TIF_NOTIFY_RESUME | \
ARCH_XFER_TO_GUEST_MODE_WORK)
struct kvm_vcpu;

3
include/linux/sched.h
View File

@ -2002,7 +2002,8 @@ static inline void set_tsk_need_resched(struct task_struct *tsk)
static inline void clear_tsk_need_resched(struct task_struct *tsk)
{
clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
atomic_long_andnot(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY,
(atomic_long_t *)&task_thread_info(tsk)->flags);
}
static inline int test_tsk_need_resched(struct task_struct *tsk)

21
include/linux/thread_info.h
View File

@ -59,6 +59,14 @@ enum syscall_work_bit {
#include <asm/thread_info.h>
#ifndef TIF_NEED_RESCHED_LAZY
#ifdef CONFIG_ARCH_HAS_PREEMPT_LAZY
#error Inconsistent PREEMPT_LAZY
#endif
#define TIF_NEED_RESCHED_LAZY TIF_NEED_RESCHED
#define _TIF_NEED_RESCHED_LAZY _TIF_NEED_RESCHED
#endif
#ifdef __KERNEL__
#ifndef arch_set_restart_data
@ -179,22 +187,27 @@ static __always_inline unsigned long read_ti_thread_flags(struct thread_info *ti
#ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H
static __always_inline bool tif_need_resched(void)
static __always_inline bool tif_test_bit(int bit)
{
return arch_test_bit(TIF_NEED_RESCHED,
return arch_test_bit(bit,
(unsigned long *)(&current_thread_info()->flags));
}
#else
static __always_inline bool tif_need_resched(void)
static __always_inline bool tif_test_bit(int bit)
{
return test_bit(TIF_NEED_RESCHED,
return test_bit(bit,
(unsigned long *)(&current_thread_info()->flags));
}
#endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
static __always_inline bool tif_need_resched(void)
{
return tif_test_bit(TIF_NEED_RESCHED);
}
#ifndef CONFIG_HAVE_ARCH_WITHIN_STACK_FRAMES
static inline int arch_within_stack_frames(const void * const stack,
const void * const stackend,

2
kernel/entry/common.c
View File

@ -98,7 +98,7 @@ __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
local_irq_enable_exit_to_user(ti_work);
if (ti_work & _TIF_NEED_RESCHED)
if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
schedule();
if (ti_work & _TIF_UPROBE)

4
kernel/entry/kvm.c
View File

@ -13,7 +13,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
return -EINTR;
}
if (ti_work & _TIF_NEED_RESCHED)
if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))
schedule();
if (ti_work & _TIF_NOTIFY_RESUME)
@ -24,7 +24,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
return ret;
ti_work = read_thread_flags();
} while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched());
} while (ti_work & XFER_TO_GUEST_MODE_WORK);
return 0;
}

34
kernel/sched/core.c
View File

@ -941,10 +941,9 @@ static inline void hrtick_rq_init(struct rq *rq)
* this avoids any races wrt polling state changes and thereby avoids
* spurious IPIs.
*/
static inline bool set_nr_and_not_polling(struct task_struct *p)
static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif)
{
struct thread_info *ti = task_thread_info(p);
return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
return !(fetch_or(&ti->flags, 1 << tif) & _TIF_POLLING_NRFLAG);
}
/*
@ -969,9 +968,9 @@ static bool set_nr_if_polling(struct task_struct *p)
}
#else
static inline bool set_nr_and_not_polling(struct task_struct *p)
static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif)
{
set_tsk_need_resched(p);
set_ti_thread_flag(ti, tif);
return true;
}
@ -1076,28 +1075,37 @@ void wake_up_q(struct wake_q_head *head)
* might also involve a cross-CPU call to trigger the scheduler on
* the target CPU.
*/
void resched_curr(struct rq *rq)
static void __resched_curr(struct rq *rq, int tif)
{
struct task_struct *curr = rq->curr;
struct thread_info *cti = task_thread_info(curr);
int cpu;
lockdep_assert_rq_held(rq);
if (test_tsk_need_resched(curr))
if (cti->flags & ((1 << tif) | _TIF_NEED_RESCHED))
return;
cpu = cpu_of(rq);
if (cpu == smp_processor_id()) {
set_tsk_need_resched(curr);
set_preempt_need_resched();
set_ti_thread_flag(cti, tif);
if (tif == TIF_NEED_RESCHED)
set_preempt_need_resched();
return;
}
if (set_nr_and_not_polling(curr))
smp_send_reschedule(cpu);
else
if (set_nr_and_not_polling(cti, tif)) {
if (tif == TIF_NEED_RESCHED)
smp_send_reschedule(cpu);
} else {
trace_sched_wake_idle_without_ipi(cpu);
}
}
void resched_curr(struct rq *rq)
{
__resched_curr(rq, TIF_NEED_RESCHED);
}
void resched_cpu(int cpu)
@ -1192,7 +1200,7 @@ static void wake_up_idle_cpu(int cpu)
* and testing of the above solutions didn't appear to report
* much benefits.
*/
if (set_nr_and_not_polling(rq->idle))
if (set_nr_and_not_polling(task_thread_info(rq->idle), TIF_NEED_RESCHED))
smp_send_reschedule(cpu);
else
trace_sched_wake_idle_without_ipi(cpu);