From d3b8f889a220aed825accc28eb64ce283a0d51ac Mon Sep 17 00:00:00 2001 From: john stultz Date: Mon, 17 Aug 2009 16:40:47 -0700 Subject: [PATCH] x86: Make tsc=reliable override boot time stability checks This patch makes the tsc=reliable option disable the boot time stability checks. Currently the option only disables the runtime watchdog checks. This change allows folks who want to override the boot time TSC stability checks and use the TSC when the system would otherwise disqualify it. There still are some situations that the TSC will be disqualified, such as cpufreq scaling. But these are situations where the box will hang if allowed. Patch also includes a fix for an issue found by Thomas Gleixner, where the TSC disqualification message wouldn't be printed after a call to unsynchronized_tsc(). Signed-off-by: John Stultz Cc: Andrew Morton Cc: akataria@vmware.com Cc: Stephen Hemminger LKML-Reference: <1250552447.7212.92.camel@localhost.localdomain> Signed-off-by: Thomas Gleixner --- Documentation/kernel-parameters.txt | 9 +++++---- arch/x86/kernel/tsc.c | 7 +++++-- 2 files changed, 10 insertions(+), 6 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 7936b801fe6a..4c6b4150266d 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2484,12 +2484,13 @@ and is between 256 and 4096 characters. It is defined in the file Format: ,,,,,,,, - tsc= Disable clocksource-must-verify flag for TSC. + tsc= Disable clocksource stability checks for TSC. Format: [x86] reliable: mark tsc clocksource as reliable, this - disables clocksource verification at runtime. - Used to enable high-resolution timer mode on older - hardware, and in virtualized environment. + disables clocksource verification at runtime, as well + as the stability checks done at bootup. Used to enable + high-resolution timer mode on older hardware, and in + virtualized environment. turbografx.map[2|3]= [HW,JOY] TurboGraFX parallel port interface diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 71f4368b357e..648fb269e5d1 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -825,6 +825,9 @@ __cpuinit int unsynchronized_tsc(void) if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) return 0; + + if (tsc_clocksource_reliable) + return 0; /* * Intel systems are normally all synchronized. * Exceptions must mark TSC as unstable: @@ -832,10 +835,10 @@ __cpuinit int unsynchronized_tsc(void) if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { /* assume multi socket systems are not synchronized: */ if (num_possible_cpus() > 1) - tsc_unstable = 1; + return 1; } - return tsc_unstable; + return 0; } static void __init init_tsc_clocksource(void)