[PATCH] x86: rewrite SMP TSC sync code

make the TSC synchronization code more robust, and unify it between x86_64 and
i386.

The biggest change is the removal of the 'fix up TSCs' code on x86_64 and
i386, in some rare cases it was /causing/ time-warps on SMP systems.

The new code only checks for TSC asynchronity - and if it can prove a
time-warp (if it can observe the TSC going backwards when going from one CPU
to another within a critical section), then the TSC clock-source is turned
off.

The TSC synchronization-checking code also got moved into a separate file.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 68 insertions, 75 deletions

diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h
index c13933185c1..e997891cc7c 100644
--- a/include/asm-i386/tsc.h
+++ b/include/asm-i386/tsc.h
@@ -1,48 +1 @@
-/*
- * linux/include/asm-i386/tsc.h
- *
- * i386 TSC related functions
- */
-#ifndef _ASM_i386_TSC_H
-#define _ASM_i386_TSC_H
-
-#include <asm/processor.h>
-
-/*
- * Standard way to access the cycle counter on i586+ CPUs.
- * Currently only used on SMP.
- *
- * If you really have a SMP machine with i486 chips or older,
- * compile for that, and this will just always return zero.
- * That's ok, it just means that the nicer scheduling heuristics
- * won't work for you.
- *
- * We only use the low 32 bits, and we'd simply better make sure
- * that we reschedule before that wraps. Scheduling at least every
- * four billion cycles just basically sounds like a good idea,
- * regardless of how fast the machine is.
- */
-typedef unsigned long long cycles_t;
-
-extern unsigned int cpu_khz;
-extern unsigned int tsc_khz;
-
-static inline cycles_t get_cycles(void)
-{
-	unsigned long long ret = 0;
-
-#ifndef CONFIG_X86_TSC
-	if (!cpu_has_tsc)
-		return 0;
-#endif
-
-#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
-	rdtscll(ret);
-#endif
-	return ret;
-}
-
-extern void tsc_init(void);
-extern void mark_tsc_unstable(void);
-
-#endif
+#include <asm-x86_64/tsc.h>
diff --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
index a6d2ff5c69b..2ce3adf7bfd 100644
--- a/include/asm-x86_64/proto.h
+++ b/include/asm-x86_64/proto.h
@@ -91,8 +91,6 @@ extern void check_efer(void);
 
 extern int unhandled_signal(struct task_struct *tsk, int sig);
 
-extern int unsynchronized_tsc(void);
-
 extern void select_idle_routine(const struct cpuinfo_x86 *c);
 
 extern unsigned long table_start, table_end;
diff --git a/include/asm-x86_64/timex.h b/include/asm-x86_64/timex.h
index b9e5320b762..a4493a77d64 100644
--- a/include/asm-x86_64/timex.h
+++ b/include/asm-x86_64/timex.h
@@ -12,35 +12,11 @@
 #include <asm/hpet.h>
 #include <asm/system.h>
 #include <asm/processor.h>
+#include <asm/tsc.h>
 #include <linux/compiler.h>
 
 #define CLOCK_TICK_RATE	PIT_TICK_RATE	/* Underlying HZ */
 
-typedef unsigned long long cycles_t;
-
-static inline cycles_t get_cycles (void)
-{
-	unsigned long long ret;
-
-	rdtscll(ret);
-	return ret;
-}
-
-/* Like get_cycles, but make sure the CPU is synchronized. */
-static __always_inline cycles_t get_cycles_sync(void)
-{
-	unsigned long long ret;
-	unsigned eax;
-	/* Don't do an additional sync on CPUs where we know
-	   RDTSC is already synchronous. */
-	alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
-			  "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
-	rdtscll(ret);
-	return ret;
-}
-
-extern unsigned int cpu_khz;
-
 extern int read_current_timer(unsigned long *timer_value);
 #define ARCH_HAS_READ_CURRENT_TIMER	1
 
diff --git a/include/asm-x86_64/tsc.h b/include/asm-x86_64/tsc.h
new file mode 100644
index 00000000000..9a0a368852c
--- /dev/null
+++ b/include/asm-x86_64/tsc.h
@@ -0,0 +1,66 @@
+/*
+ * linux/include/asm-x86_64/tsc.h
+ *
+ * x86_64 TSC related functions
+ */
+#ifndef _ASM_x86_64_TSC_H
+#define _ASM_x86_64_TSC_H
+
+#include <asm/processor.h>
+
+/*
+ * Standard way to access the cycle counter.
+ */
+typedef unsigned long long cycles_t;
+
+extern unsigned int cpu_khz;
+extern unsigned int tsc_khz;
+
+static inline cycles_t get_cycles(void)
+{
+	unsigned long long ret = 0;
+
+#ifndef CONFIG_X86_TSC
+	if (!cpu_has_tsc)
+		return 0;
+#endif
+
+#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
+	rdtscll(ret);
+#endif
+	return ret;
+}
+
+/* Like get_cycles, but make sure the CPU is synchronized. */
+static __always_inline cycles_t get_cycles_sync(void)
+{
+	unsigned long long ret;
+#ifdef X86_FEATURE_SYNC_RDTSC
+	unsigned eax;
+
+	/*
+	 * Don't do an additional sync on CPUs where we know
+	 * RDTSC is already synchronous:
+	 */
+	alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
+			  "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
+#else
+	sync_core();
+#endif
+	rdtscll(ret);
+
+	return ret;
+}
+
+extern void tsc_init(void);
+extern void mark_tsc_unstable(void);
+extern int unsynchronized_tsc(void);
+
+/*
+ * Boot-time check whether the TSCs are synchronized across
+ * all CPUs/cores:
+ */
+extern void check_tsc_sync_source(int cpu);
+extern void check_tsc_sync_target(void);
+
+#endif