[Skiboot] [PATCH v2 08/25] fast-reboot: add sreset timeout detection and handling

[Nicholas Piggin]

Have the initiator wait for all its sreset targets to call in, and
time out after 200ms if they did not. Fail and revert to IPL reboot.

Testing indicates that after successful sreset_all_others(), it
takes less than 102ms (in hundreds of fast reboots) for secondaries
to call in. 100 of that is due to an initial delay, but core
un-splitting was not measured.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 core/fast-reboot.c | 78 +++++++++++++++++++++++++++++++-----------------------
 1 file changed, 45 insertions(+), 33 deletions(-)

diff --git a/core/fast-reboot.c b/core/fast-reboot.c
index c6ecd1cc6..70fb4eb9f 100644
--- a/core/fast-reboot.c
+++ b/core/fast-reboot.c
@@ -340,6 +340,35 @@ static bool fast_reset_p8(void)
 	return false;
 }
 
+static bool cpu_state_wait_all_others(enum cpu_thread_state state,
+					unsigned long timeout_tb)
+{
+	struct cpu_thread *cpu;
+	unsigned long end = mftb() + timeout_tb;
+
+	sync();
+	for_each_ungarded_cpu(cpu) {
+		if (cpu == this_cpu())
+			continue;
+
+		if (cpu->state != state) {
+			smt_lowest();
+			while (cpu->state != state) {
+				barrier();
+
+				if (timeout_tb && (tb_compare(mftb(), end) == TB_AAFTERB)) {
+					smt_medium();
+					return false;
+				}
+			}
+			smt_medium();
+		}
+	}
+	sync();
+
+	return true;
+}
+
 extern void *fdt;
 extern struct lock capi_lock;
 
@@ -401,11 +430,16 @@ void fast_reboot(void)
 	/* Unlock, at this point we go away */
 	unlock(&reset_lock);
 
-	if (success) {
-		asm volatile("ba	0x100\n\t" : : : "memory");
-		for (;;)
-			;
-	}
+	if (!success)
+		return;
+
+	/* Ensure all the sresets get through */
+	if (!cpu_state_wait_all_others(cpu_state_present, msecs_to_tb(200)))
+		return;
+
+	asm volatile("ba	0x100\n\t" : : : "memory");
+	for (;;)
+		;
 }
 
 static void cleanup_cpu_state(void)
@@ -497,8 +531,6 @@ void __noreturn fast_reboot_entry(void);
 
 void __noreturn fast_reboot_entry(void)
 {
-	struct cpu_thread *cpu;
-
 	prlog(PR_DEBUG, "RESET: CPU 0x%04x reset in\n", this_cpu()->pir);
 	time_wait_ms(100);
 
@@ -512,13 +544,15 @@ void __noreturn fast_reboot_entry(void)
 	 */
 	check_split_core();
 
+	sync();
+	this_cpu()->state = cpu_state_present;
+	sync();
+
 	/* Are we the original boot CPU ? If not, we spin waiting
 	 * for a relase signal from CPU 1, then we clean ourselves
 	 * up and go processing jobs.
 	 */
 	if (this_cpu() != boot_cpu) {
-		this_cpu()->state = cpu_state_present;
-		sync();
 		if (!fast_boot_release) {
 			smt_lowest();
 			while (!fast_boot_release)
@@ -535,18 +569,7 @@ void __noreturn fast_reboot_entry(void)
 	/* We are the original boot CPU, wait for secondaries to
 	 * be captured.
 	 */
-	for_each_ungarded_cpu(cpu) {
-		if (cpu == this_cpu())
-			continue;
-
-		/* XXX Add a callin timeout ? */
-		if (cpu->state != cpu_state_present) {
-			smt_lowest();
-			while (cpu->state != cpu_state_present)
-				barrier();
-			smt_medium();
-		}
-	}
+	cpu_state_wait_all_others(cpu_state_present, 0);
 
 	prlog(PR_INFO, "RESET: Releasing secondaries...\n");
 
@@ -555,18 +578,7 @@ void __noreturn fast_reboot_entry(void)
 	sync();
 
 	/* Wait for them to respond */
-	for_each_ungarded_cpu(cpu) {
-		if (cpu == this_cpu())
-			continue;
-
-		/* XXX Add a callin timeout ? */
-		if (cpu->state == cpu_state_present) {
-			smt_lowest();
-			while (cpu->state == cpu_state_present)
-				barrier();
-			smt_medium();
-		}
-	}
+	cpu_state_wait_all_others(cpu_state_active, 0);
 
 	prlog(PR_DEBUG, "RESET: Releasing special wakeups...\n");
 
-- 
2.15.0