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entry: Hook up rseq time slice extension

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Wire the grant decision function up in exit_to_user_mode_loop()

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155709.258157362@linutronix.de
This commit is contained in:
Thomas Gleixner 2025-12-15 17:52:31 +01:00 • committed by Peter Zijlstra
parent dfb630f548
commit 3c78aaec19
1 changed files with 25 additions and 2 deletions
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27
kernel/entry/common.c
View file

@ -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))
schedule();
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);