MCS, SMP: Add clock synchronisation test

Because ksCurTime is compared cross-node now, time across
nodes must be the same. Check this once during boot.

Replace __atomic_signal_fence with the more correct
__atomic_thread_fence, as ksNumCPUs will be changed
cross-node.

Signed-off-by: Indan Zupancic <Indan.Zupancic@mep-info.com>

include/kernel/boot.h

@@ -135,3 +135,14 @@ static inline BOOT_CODE pptr_t it_alloc_paging(void)
 
 /* return the amount of paging structures required to cover v_reg */
 word_t arch_get_n_paging(v_region_t it_veg);
+
+#if defined(CONFIG_DEBUG_BUILD) && defined(ENABLE_SMP_SUPPORT) && defined(CONFIG_KERNEL_MCS)
+/* Test whether clocks are synchronised across nodes */
+#define ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+#endif
+
+#ifdef ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+BOOT_CODE void clock_sync_test(void);
+#else
+#define clock_sync_test()
+#endif

src/arch/arm/kernel/boot.c

@@ -274,6 +274,7 @@ BOOT_CODE static bool_t try_init_kernel_secondary_core(void)
 #endif /* CONFIG_ARM_HYPERVISOR_SUPPORT */
     NODE_LOCK_SYS;
 
+    clock_sync_test();
     ksNumCPUs++;
 
     init_core_state(SchedulerAction_ResumeCurrentThread);
@@ -303,8 +304,11 @@ BOOT_CODE static void release_secondary_cpus(void)
 
     /* Wait until all the secondary cores are done initialising */
     while (ksNumCPUs != CONFIG_MAX_NUM_NODES) {
-        /* perform a memory release+acquire to get new values of ksNumCPUs */
-        __atomic_signal_fence(__ATOMIC_ACQ_REL);
+#ifdef ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+        NODE_STATE(ksCurTime) = getCurrentTime();
+#endif
+        /* perform a memory acquire to get new values of ksNumCPUs, release for ksCurTime */
+        __atomic_thread_fence(__ATOMIC_ACQ_REL);
     }
 }
 #endif /* ENABLE_SMP_SUPPORT */

src/arch/riscv/kernel/boot.c

@@ -159,6 +159,7 @@ BOOT_CODE static bool_t try_init_kernel_secondary_core(word_t hart_id, word_t co
     init_cpu();
     NODE_LOCK_SYS;
 
+    clock_sync_test();
     ksNumCPUs++;
     init_core_state(SchedulerAction_ResumeCurrentThread);
     ifence_local();
@@ -171,11 +172,14 @@ BOOT_CODE static void release_secondary_cores(void)
     fence_w_r();
 
     while (ksNumCPUs != CONFIG_MAX_NUM_NODES) {
-        __atomic_signal_fence(__ATOMIC_ACQ_REL);
+#ifdef ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+        NODE_STATE(ksCurTime) = getCurrentTime();
+#endif
+        __atomic_thread_fence(__ATOMIC_ACQ_REL);
     }
 }
+#endif /* ENABLE_SMP_SUPPORT */
 
-#endif
 /* Main kernel initialisation function. */
 
 static BOOT_CODE bool_t try_init_kernel(

src/arch/x86/kernel/smp_sys.c

@@ -6,6 +6,7 @@
 
 #include <config.h>
 #include <arch/machine.h>
+#include <arch/machine/timer.h>
 #include <arch/kernel/boot_sys.h>
 #include <arch/kernel/smp_sys.h>
 #include <smp/lock.h>
@@ -64,7 +65,12 @@ BOOT_CODE void start_boot_aps(void)
         start_cpu(boot_state.cpus[current_ap_index], BOOT_NODE_PADDR);
 
         /* wait for current AP to boot up */
-        while (smp_aps_index == current_ap_index);
+        while (smp_aps_index == current_ap_index) {
+#ifdef ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+            NODE_STATE(ksCurTime) = getCurrentTime();
+            __atomic_thread_fence(__ATOMIC_ACQ_REL);
+#endif
+        }
     }
 }
 
@@ -126,6 +132,7 @@ VISIBLE void boot_node(void)
         fail("boot_node failed for some reason :(\n");
     }
 
+    clock_sync_test();
     smp_aps_index++;
 
     /* grab BKL before leaving the kernel */

src/kernel/boot.c

@@ -553,6 +553,26 @@ BOOT_CODE tcb_t *create_initial_thread(cap_t root_cnode_cap, cap_t it_pd_cap, vp
     return tcb;
 }
 
+#ifdef ENABLE_SMP_CLOCK_SYNC_TEST_ON_BOOT
+BOOT_CODE void clock_sync_test(void)
+{
+    ticks_t t, t0;
+    ticks_t margin = usToTicks(1) + getTimerPrecision();
+
+    assert(getCurrentCPUIndex() != 0);
+    t = NODE_STATE_ON_CORE(ksCurTime, 0);
+    do {
+        /* perform a memory acquire to get new values of ksCurTime */
+        __atomic_thread_fence(__ATOMIC_ACQUIRE);
+        t0 = NODE_STATE_ON_CORE(ksCurTime, 0);
+    } while (t0 == t);
+    t = getCurrentTime();
+    printf("clock_sync_test[%d]: t0 = %"PRIu64", t = %"PRIu64", td = %"PRIi64"\n",
+           (int)getCurrentCPUIndex(), t0, t, t - t0);
+    assert(t0 <= margin + t && t <= t0 + margin);
+}
+#endif
+
 BOOT_CODE void init_core_state(tcb_t *scheduler_action)
 {
 #ifdef CONFIG_HAVE_FPU