[XenPPC] [PATCH] Fix IPI stall timeout without using timebase_freq

[Amos Waterland <apw@xxxxxxxxxx>]

When using the register dump feature of Xen, one will sometimes see a
message about an IPI finish stall.  This is because of an int to long
comparison bug, so fix it by doing proper nanosecond based time
accounting with no explicit reference to timebase_freq.

Signed-off-by: Amos Waterland <apw@xxxxxxxxxx>

---

 smp.c |   39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff -r e01e08ca629b xen/arch/powerpc/smp.c
--- a/xen/arch/powerpc/smp.c    Tue Nov 28 17:01:00 2006 -0500
+++ b/xen/arch/powerpc/smp.c    Tue Nov 28 18:28:35 2006 -0500
@@ -90,7 +90,8 @@ int on_selected_cpus(
     int retry,
     int wait)
 {
-    int t, retval = 0, nr_cpus = cpus_weight(selected);
+    int retval = 0, nr_cpus = cpus_weight(selected);
+    unsigned long start, stall = SECONDS(1);
 
     spin_lock(&call_lock);
 
@@ -104,19 +105,21 @@ int on_selected_cpus(
     send_IPI_mask(selected, CALL_FUNCTION_VECTOR);
 
     /* We always wait for an initiation ACK from remote CPU.  */
-    for (t = 0; atomic_read(&call_data.started) != nr_cpus; t++) {
-        if (t && t % timebase_freq == 0) {
+    for (start = NOW(); atomic_read(&call_data.started) != nr_cpus; ) {
+        if (NOW() > start + stall) {
             printk("IPI start stall: %d ACKS to %d SYNS\n", 
                    atomic_read(&call_data.started), nr_cpus);
+           start = NOW();
         }
     }
 
     /* If told to, we wait for a completion ACK from remote CPU.  */
     if (wait) {
-        for (t = 0; atomic_read(&call_data.finished) != nr_cpus; t++) {
-            if (t > timebase_freq && t % timebase_freq == 0) {
+        for (start = NOW(); atomic_read(&call_data.finished) != nr_cpus; ) {
+            if (NOW() > start + stall) {
                 printk("IPI finish stall: %d ACKS to %d SYNS\n", 
                        atomic_read(&call_data.finished), nr_cpus);
+                start = NOW();
             }
         }
     }
@@ -168,6 +171,11 @@ void smp_message_recv(int msg, struct cp
 #ifdef DEBUG_IPI
 static void debug_ipi_ack(void *info)
 {
+    if (info) {
+       unsigned long start, stall = SECONDS(5);
+       for (start = NOW(); NOW() < start + stall; );
+       printk("IPI recv on cpu #%d: %s\n", smp_processor_id(), (char *)info);
+    }
     return;
 }
 
@@ -175,12 +183,12 @@ void ipi_torture_test(void)
 {
     int cpu;
     unsigned long before, after, delta;
-    unsigned long min = ~0, max = 0, mean = 0, sum = 0, tick = 0;
+    unsigned long min = ~0, max = 0, mean = 0, sum = 0, trials = 0;
     cpumask_t mask;
 
     cpus_clear(mask);
 
-    while (tick < 1000000) {
+    while (trials < 1000000) {
         for_each_online_cpu(cpu) {
             cpu_set(cpu, mask);
             before = mftb();
@@ -192,12 +200,15 @@ void ipi_torture_test(void)
             if (delta > max) max = delta;
             if (delta < min) min = delta;
             sum += delta;
-            tick++;
-        }
-    }
-
-    mean = sum / tick;
-
-    printk("IPI tb ticks: min = %ld max = %ld mean = %ld\n", min, max, mean);
+            trials++;
+        }
+    }
+
+    mean = tb_to_ns(sum / trials);
+
+    printk("IPI latency: min = %ld ticks, max = %ld ticks, mean = %ldns\n",
+          min, max, mean);
+
+    smp_call_function(debug_ipi_ack, "Hi", 0, 1);
 }
 #endif

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