kernel: Add CONFIG_SCHED_IPI_CASCADE
When this new Kconfig option is enabled, preempted threads on an SMP
system may generate additional IPIs when they are switched out.
Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
diff --git a/kernel/Kconfig.smp b/kernel/Kconfig.smp
index da83d16..624d13c 100644
--- a/kernel/Kconfig.smp
+++ b/kernel/Kconfig.smp
@@ -63,6 +63,18 @@
thread to take an interrupt, which can be arbitrarily far in the
future).
+config SCHED_IPI_CASCADE
+ bool "Use cascading IPIs to correct localized scheduling"
+ depends on SCHED_CPU_MASK && !SCHED_CPU_MASK_PIN_ONLY
+ default n
+ help
+ Threads that are preempted by a local thread (a thread that is
+ restricted by its CPU mask to execute on a subset of all CPUs) may
+ trigger additional IPIs when the preempted thread is of higher
+ priority than a currently executing thread on another CPU. Although
+ these cascading IPIs will ensure that the system will settle upon a
+ valid set of high priority threads, it comes at a performance cost.
+
config TRACE_SCHED_IPI
bool "Test IPI"
help
diff --git a/kernel/sched.c b/kernel/sched.c
index 8cd401b..501b273 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -931,12 +931,15 @@
z_sched_usage_switch(new_thread);
if (old_thread != new_thread) {
+ uint8_t cpu_id;
+
update_metairq_preempt(new_thread);
z_sched_switch_spin(new_thread);
arch_cohere_stacks(old_thread, interrupted, new_thread);
_current_cpu->swap_ok = 0;
- new_thread->base.cpu = arch_curr_cpu()->id;
+ cpu_id = arch_curr_cpu()->id;
+ new_thread->base.cpu = cpu_id;
set_current(new_thread);
#ifdef CONFIG_TIMESLICING
@@ -959,6 +962,12 @@
* will not return into it.
*/
if (z_is_thread_queued(old_thread)) {
+#ifdef CONFIG_SCHED_IPI_CASCADE
+ if ((new_thread->base.cpu_mask != -1) &&
+ (old_thread->base.cpu_mask != BIT(cpu_id))) {
+ flag_ipi(ipi_mask_create(old_thread));
+ }
+#endif
runq_add(old_thread);
}
}
