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kernel/sched: Close hole with cross-core timeslice expirations

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Moving timeslice events to timeouts isn't quite enough on SMP, as it's
still possible for systems that don't broadcast their timer interrupts
to end up handling an expiration for a foreign CPU.  There, we need an
IPI, and a symmetric call to z_time_slice() (which is itempotent and
fast) in the IPI ISR.

Signed-off-by: Andy Ross <andyross@google.com>
This commit is contained in:
Andy Ross 2023-03-07 08:29:31 -08:00 committed by Carles Cufí
parent f3afd5a4c9
commit c5c3ad95de
1 changed files with 23 additions and 9 deletions
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32
kernel/sched.c
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@ -401,6 +401,15 @@ static void move_thread_to_end_of_prio_q(struct k_thread *thread)
update_cache(thread == _current);
}
static void flag_ipi(void)
{
#if defined(CONFIG_SMP) && defined(CONFIG_SCHED_IPI_SUPPORTED)
if (arch_num_cpus() > 1) {
_kernel.pending_ipi = true;
}
#endif
}
#ifdef CONFIG_TIMESLICING
static int slice_ticks;
@ -434,6 +443,14 @@ static void slice_timeout(struct _timeout *t)
int cpu = ARRAY_INDEX(slice_timeouts, t);
slice_expired[cpu] = true;
/* We need an IPI if we just handled a timeslice expiration
* for a different CPU. Ideally this would be able to target
* the specific core, but that's not part of the API yet.
*/
if (IS_ENABLED(CONFIG_SMP) && cpu != _current_cpu->id) {
flag_ipi();
}
}
void z_reset_time_slice(struct k_thread *curr)
@ -604,15 +621,6 @@ static bool thread_active_elsewhere(struct k_thread *thread)
return false;
}
static void flag_ipi(void)
{
#if defined(CONFIG_SMP) && defined(CONFIG_SCHED_IPI_SUPPORTED)
if (arch_num_cpus() > 1) {
_kernel.pending_ipi = true;
}
#endif
}
static void ready_thread(struct k_thread *thread)
{
#ifdef CONFIG_KERNEL_COHERENCE
@ -1553,6 +1561,12 @@ void z_sched_ipi(void)
#ifdef CONFIG_TRACE_SCHED_IPI
z_trace_sched_ipi();
#endif
#ifdef CONFIG_TIMESLICING
if (slice_time(_current) && sliceable(_current)) {
z_time_slice();
}
#endif
}
#endif