From 0b0f535c66ed2dfd085d13ace37d7810525eaf6a Mon Sep 17 00:00:00 2001
From: hujun5 <hujun5@xiaomi.com>
Date: Fri, 16 Aug 2024 16:46:20 +0800
Subject: [PATCH] sched: replace sync pause with async pause for setpriority

reason:
In the kernel, we are planning to remove all occurrences of up_cpu_pause as one of the steps to
simplify the implementation of critical sections. The goal is to enable spin_lock_irqsave to encapsulate critical sections,
thereby facilitating the replacement of critical sections(big lock) with smaller spin_lock_irqsave(small lock)

Configuring NuttX and compile:
$ ./tools/configure.sh -l qemu-armv8a:nsh_smp
$ make
Running with qemu
$ qemu-system-aarch64 -cpu cortex-a53 -smp 4 -nographic
-machine virt,virtualization=on,gic-version=3
-net none -chardev stdio,id=con,mux=on -serial chardev:con
-mon chardev=con,mode=readline -kernel ./nuttx

Signed-off-by: hujun5 <hujun5@xiaomi.com>
---
 sched/sched/sched_setpriority.c | 76 +++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/sched/sched/sched_setpriority.c b/sched/sched/sched_setpriority.c
index 7a3d5bfd33349..fe788c8270910 100644
--- a/sched/sched/sched_setpriority.c
+++ b/sched/sched/sched_setpriority.c
@@ -37,10 +37,58 @@
 #include "irq/irq.h"
 #include "sched/sched.h"
 
+/****************************************************************************
+ * Private Type Declarations
+ ****************************************************************************/
+
+#ifdef CONFIG_SMP
+struct reprioritize_arg_s
+{
+  pid_t pid;
+  cpu_set_t saved_affinity;
+  uint16_t saved_flags;
+  int  sched_priority;
+  bool need_restore;
+};
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
 
+static int reprioritize_handler(FAR void *cookie)
+{
+  FAR struct reprioritize_arg_s *arg = cookie;
+  FAR struct tcb_s *rtcb = this_task();
+  FAR struct tcb_s *tcb;
+  irqstate_t flags;
+
+  flags = enter_critical_section();
+
+  tcb = nxsched_get_tcb(arg->pid);
+
+  if (!tcb || tcb->task_state == TSTATE_TASK_INVALID ||
+      (tcb->flags & TCB_FLAG_EXIT_PROCESSING) != 0)
+    {
+      leave_critical_section(flags);
+      return OK;
+    }
+
+  if (arg->need_restore)
+    {
+      tcb->affinity = arg->saved_affinity;
+      tcb->flags = arg->saved_flags;
+    }
+
+  if (nxsched_reprioritize_rtr(tcb, arg->sched_priority))
+    {
+      up_switch_context(this_task(), rtcb);
+    }
+
+  leave_critical_section(flags);
+  return OK;
+}
+#endif
+
 /****************************************************************************
  * Name: nxsched_nexttcb
  *
@@ -175,6 +223,34 @@ static inline void nxsched_running_setpriority(FAR struct tcb_s *tcb,
         {
           /* A context switch will occur. */
 
+#ifdef CONFIG_SMP
+          if (tcb->cpu != this_cpu() &&
+              tcb->task_state == TSTATE_TASK_RUNNING)
+            {
+              struct reprioritize_arg_s arg;
+
+              if ((tcb->flags & TCB_FLAG_CPU_LOCKED) != 0)
+                {
+                  arg.pid = tcb->pid;
+                  arg.need_restore = false;
+                }
+              else
+                {
+                  arg.pid = tcb->pid;
+                  arg.saved_flags = tcb->flags;
+                  arg.saved_affinity = tcb->affinity;
+                  arg.need_restore = true;
+
+                  tcb->flags |= TCB_FLAG_CPU_LOCKED;
+                  CPU_SET(tcb->cpu, &tcb->affinity);
+                }
+
+              arg.sched_priority = sched_priority;
+              nxsched_smp_call_single(tcb->cpu, reprioritize_handler,
+                                      &arg, true);
+            }
+          else
+#endif
           if (nxsched_reprioritize_rtr(tcb, sched_priority))
             {
               up_switch_context(this_task(), rtcb);