From: compudj <compudj@04897980-b3bd-0310-b5e0-8ef037075253>
Date: Mon, 19 Mar 2007 03:56:03 +0000 (+0000)
Subject: add teest tsc sync
X-Git-Tag: v0.12.20~1052
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=9100d218cdd6d5be6aa7801c8495aa1706b23ed3;p=lttv.git

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
index 00000000..16fcf376
--- /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");
+