add teest tsc sync

git-svn-id: http://ltt.polymtl.ca/svn@2437 04897980-b3bd-0310-b5e0-8ef037075253

diff --git a/tests/kernel/test-async-tsc.c b/tests/kernel/test-async-tsc.c
new file mode 100644 (file)
index 0000000..16fcf37
--- /dev/null
+++ b/tests/kernel/test-async-tsc.c
@@ -0,0 +1,83 @@
+/* test-async-tsc.c
+ *
+ * test async tsc on AMD.
+ */
+
+
+#include <asm/atomic.h>
+#include <linux/module.h>
+#include <asm/timex.h>
+
+//LTT #define LTT_MIN_PROBE_DURATION 400
+//get_cycles
+#define LTT_MIN_PROBE_DURATION 200
+
+static atomic_long_t ltt_last_tsc = ATOMIC_LONG_INIT(0);
+
+/* When the local TSC is discovered to lag behind the highest TSC counter, we
+ * increment the TSC count of an amount that should be, ideally, lower than the
+ * execution time of this routine, in cycles : this is the granularity we look
+ * for : we must be able to order the events. */
+
+cycles_t ltt_tsc_read(void)
+{
+       cycles_t new_tsc;
+       cycles_t last_tsc;
+
+       new_tsc = get_cycles_sync();
+        if (cpu_has(&cpu_data[smp_processor_id()], X86_FEATURE_CONSTANT_TSC))
+                return new_tsc;
+
+       do {
+               last_tsc = atomic_long_read(&ltt_last_tsc);
+               if (new_tsc < last_tsc) {
+                       /* last_tsc may only have incremented since last read,
+                        * therefore the condition new_tsc < last_tsc still
+                        * applies even if it has been updated. Therefore, we
+                        * can use add_return, cheaper than cmpxchg here. */
+                       new_tsc = atomic_long_add_return(LTT_MIN_PROBE_DURATION,
+                                       &ltt_last_tsc);
+                       break;
+               }
+               /* cmpxchg will fail if ltt_last_tsc has been concurrently
+                * updated by add_return or set to a lower tsc value by a
+                * concurrent CPU at the same time. cmpxchg will succeed if
+                * the other CPUs update the ltt_last_tsc with a cmpxchg or
+                * add_return to a value higher than the new_tsc : it's ok
+                * since the current get_cycles happened before the one that
+                * causes the ltt_last_tsc to become higher than new_tsc.
+                * It also succeeds if we write to the memory location
+                * successfully without concurrent modification. */
+       } while (atomic_long_cmpxchg(&ltt_last_tsc, last_tsc, new_tsc)
+               < new_tsc);
+       return new_tsc;
+}
+
+static int __init test_init(void)
+{
+       int i;
+       cycles_t time1, time2;
+       volatile cycles_t myval;
+
+       time1 = get_cycles();
+       for (i=0; i<200; i++) {
+               //printk("time %llu\n", ltt_tsc_read());
+               //myval = ltt_tsc_read();
+               myval = get_cycles_sync();
+       }
+       time2 = get_cycles();
+       printk("timediff %llu\n", time2-time1);
+       return -EPERM;
+}
+
+static void __exit test_exit(void)
+{
+}
+
+module_init(test_init);
+module_exit(test_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mathieu Desnoyers");
+MODULE_DESCRIPTION("sync async tsc");
+