Commit a43b4856 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

hrtimer: Prepare stubs for deferred rearming 



The hrtimer interrupt expires timers and at the end of the interrupt it
rearms the clockevent device for the next expiring timer.

That's obviously correct, but in the case that a expired timer set
NEED_RESCHED the return from interrupt ends up in schedule(). If HRTICK is
enabled then schedule() will modify the hrtick timer, which causes another
reprogramming of the hardware.

That can be avoided by deferring the rearming to the return from interrupt
path and if the return results in a immediate schedule() invocation then it
can be deferred until the end of schedule().

To make this correct the affected code parts need to be made aware of this.

Provide empty stubs for the deferred rearming mechanism, so that the
relevant code changes for entry, softirq and scheduler can be split up into
separate changes independent of the actual enablement in the hrtimer code.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260224163431.000891171@kernel.org
parent 9e07a9c9

include/linux/hrtimer.h

+1 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#define _LINUX_HRTIMER_H



#include <linux/hrtimer_defs.h>

#include <linux/hrtimer_rearm.h>

#include <linux/hrtimer_types.h>

#include <linux/init.h>

#include <linux/list.h>

include/linux/hrtimer_rearm.h

0 → 100644
+21 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#ifndef _LINUX_HRTIMER_REARM_H

#define _LINUX_HRTIMER_REARM_H



#ifdef CONFIG_HRTIMER_REARM_DEFERRED

static __always_inline void __hrtimer_rearm_deferred(void) { }

static __always_inline void hrtimer_rearm_deferred(void) { }

static __always_inline void hrtimer_rearm_deferred_tif(unsigned long tif_work) { }

static __always_inline bool

hrtimer_rearm_deferred_user_irq(unsigned long *tif_work, const unsigned long tif_mask) { return false; }

static __always_inline bool hrtimer_test_and_clear_rearm_deferred(void) { return false; }

#else  /* CONFIG_HRTIMER_REARM_DEFERRED */

static __always_inline void __hrtimer_rearm_deferred(void) { }

static __always_inline void hrtimer_rearm_deferred(void) { }

static __always_inline void hrtimer_rearm_deferred_tif(unsigned long tif_work) { }

static __always_inline bool

hrtimer_rearm_deferred_user_irq(unsigned long *tif_work, const unsigned long tif_mask) { return false; }

static __always_inline bool hrtimer_test_and_clear_rearm_deferred(void) { return false; }

#endif  /* !CONFIG_HRTIMER_REARM_DEFERRED */



#endif

kernel/time/Kconfig

+4 −0
Original line number Diff line number Diff line
@@ -58,6 +58,10 @@ config GENERIC_CLOCKEVENTS_COUPLED_INLINE 
config GENERIC_CMOS_UPDATE

	bool



# Deferred rearming of the hrtimer interrupt

config HRTIMER_REARM_DEFERRED

       def_bool n



# Select to handle posix CPU timers from task_work

# and not from the timer interrupt context

config HAVE_POSIX_CPU_TIMERS_TASK_WORK