Commit 3c78aaec authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

entry: Hook up rseq time slice extension 



Wire the grant decision function up in exit_to_user_mode_loop()

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155709.258157362@linutronix.de
parent dfb630f5

kernel/entry/common.c

+25 −2
Original line number Diff line number Diff line
@@ -17,6 +17,27 @@ void __weak arch_do_signal_or_restart(struct pt_regs *regs) { } 
#define EXIT_TO_USER_MODE_WORK_LOOP	(EXIT_TO_USER_MODE_WORK)

#endif



/* TIF bits, which prevent a time slice extension. */

#ifdef CONFIG_PREEMPT_RT

/*

 * Since rseq slice ext has a direct correlation to the worst case

 * scheduling latency (schedule is delayed after all), only have it affect

 * LAZY reschedules on PREEMPT_RT for now.

 *

 * However, since this delay is only applicable to userspace, a value

 * for rseq_slice_extension_nsec that is strictly less than the worst case

 * kernel space preempt_disable() region, should mean the scheduling latency

 * is not affected, even for !LAZY.

 *

 * However, since this value depends on the hardware at hand, it cannot be

 * pre-determined in any sensible way. Hence punt on this problem for now.

 */

# define TIF_SLICE_EXT_SCHED	(_TIF_NEED_RESCHED_LAZY)

#else

# define TIF_SLICE_EXT_SCHED	(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)

#endif

#define TIF_SLICE_EXT_DENY	(EXIT_TO_USER_MODE_WORK & ~TIF_SLICE_EXT_SCHED)



static __always_inline unsigned long __exit_to_user_mode_loop(struct pt_regs *regs,

							      unsigned long ti_work)

{
@@ -28,8 +49,10 @@ static __always_inline unsigned long __exit_to_user_mode_loop(struct pt_regs *re 


		local_irq_enable_exit_to_user(ti_work);



		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY))

		if (ti_work & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) {

			if (!rseq_grant_slice_extension(ti_work & TIF_SLICE_EXT_DENY))

				schedule();

		}



		if (ti_work & _TIF_UPROBE)

			uprobe_notify_resume(regs);