x86/tsc: Disable clocksource watchdog for TSC on qualified platorms

[sfrench/cifs-2.6.git] / arch / x86 / kernel / tsc.c

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 2e076a459a0c084aa279f32f3fc644604713e595..a698196377be9bf650eb8bc1ea28692068568626 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1180,6 +1180,12 @@ void mark_tsc_unstable(char *reason)
 
 EXPORT_SYMBOL_GPL(mark_tsc_unstable);
 
+static void __init tsc_disable_clocksource_watchdog(void)
+{
+       clocksource_tsc_early.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
+       clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
+}
+
 static void __init check_system_tsc_reliable(void)
 {
 #if defined(CONFIG_MGEODEGX1) || defined(CONFIG_MGEODE_LX) || defined(CONFIG_X86_GENERIC)
@@ -1196,6 +1202,23 @@ static void __init check_system_tsc_reliable(void)
 #endif
        if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
                tsc_clocksource_reliable = 1;
+
+       /*
+        * Disable the clocksource watchdog when the system has:
+        *  - TSC running at constant frequency
+        *  - TSC which does not stop in C-States
+        *  - the TSC_ADJUST register which allows to detect even minimal
+        *    modifications
+        *  - not more than two sockets. As the number of sockets cannot be
+        *    evaluated at the early boot stage where this has to be
+        *    invoked, check the number of online memory nodes as a
+        *    fallback solution which is an reasonable estimate.
+        */
+       if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+           boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
+           boot_cpu_has(X86_FEATURE_TSC_ADJUST) &&
+           nr_online_nodes <= 2)
+               tsc_disable_clocksource_watchdog();
 }
 
 /*
@@ -1387,9 +1410,6 @@ static int __init init_tsc_clocksource(void)
        if (tsc_unstable)
                goto unreg;
 
-       if (tsc_clocksource_reliable || no_tsc_watchdog)
-               clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
-
        if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
                clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
 
@@ -1527,7 +1547,7 @@ void __init tsc_init(void)
        }
 
        if (tsc_clocksource_reliable || no_tsc_watchdog)
-               clocksource_tsc_early.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
+               tsc_disable_clocksource_watchdog();
 
        clocksource_register_khz(&clocksource_tsc_early, tsc_khz);
        detect_art();