From eca0cd028bdf0f6aaceb0d023e9c7501079a7dda Mon Sep 17 00:00:00 2001 From: Alok Kataria Date: Fri, 31 Oct 2008 12:01:58 -0700 Subject: x86: Add a synthetic TSC_RELIABLE feature bit. Impact: Changes timebase calibration on Vmware. Use the synthetic TSC_RELIABLE bit to workaround virtualization anomalies. Virtual TSCs can be kept nearly in sync, but because the virtual TSC offset is set by software, it's not perfect. So, the TSC synchronization test can fail. Even then the TSC can be used as a clocksource since the VMware platform exports a reliable TSC to the guest for timekeeping purposes. Use this bit to check if we need to skip the TSC sync checks. Along with this also set the CONSTANT_TSC bit when on VMware, since we still want to use TSC as clocksource on VM running over hardware which has unsynchronized TSC's (opteron's), since the hypervisor will take care of providing consistent TSC to the guest. Signed-off-by: Alok N Kataria Signed-off-by: Dan Hecht Signed-off-by: H. Peter Anvin --- arch/x86/kernel/tsc_sync.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'arch/x86/kernel/tsc_sync.c') diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 9ffb01c31c40..5977c40a138f 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -108,6 +108,12 @@ void __cpuinit check_tsc_sync_source(int cpu) if (unsynchronized_tsc()) return; + if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) { + printk(KERN_INFO + "Skipping synchronization checks as TSC is reliable.\n"); + return; + } + printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:", smp_processor_id(), cpu); @@ -161,7 +167,7 @@ void __cpuinit check_tsc_sync_target(void) { int cpus = 2; - if (unsynchronized_tsc()) + if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) return; /* -- cgit v1.2.2