Messages in this thread Patch in this message | | | Subject | [Patch] Skip cpu_calibrate for kernel running under hypervisors. | From | Alok Kataria <> | Date | Mon, 16 Aug 2010 12:25:54 -0700 |
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Hi,
This is a trivial change to fix the cpu_khz value returned when running on a virtualized environment. We have seen instances when the cpu_khz value is off by couple of MHz's when running on VMware's platform on AMD hardware.
-- Since the TSC frequency read from hypervisor is accurate for the guest, and since the hypervisor will always clock the vcpu at the TSC frequency, there is no need to calibrate it again. To avoid any calibration errors through calibrate_cpu this patch skips calling calibrate_cpu for kernel running under hypervisors.
Signed-off-by: Alok N Kataria <akataria@vmware.com> Cc: K. Y. Srinivasan <ksrinivasan@novell.com> Cc: Greg KH <greg@kroah.com> Cc: H. Peter Anvin <hpa@zytor.com>
Index: linux-x86-tree.git/arch/x86/kernel/tsc.c =================================================================== --- linux-x86-tree.git.orig/arch/x86/kernel/tsc.c 2010-08-03 12:21:20.000000000 -0700 +++ linux-x86-tree.git/arch/x86/kernel/tsc.c 2010-08-13 15:07:08.000000000 -0700 @@ -927,7 +927,7 @@ void __init tsc_init(void) } if (cpu_has(&boot_cpu_data, X86_FEATURE_CONSTANT_TSC) && - (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)) + (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && !x86_hyper) cpu_khz = calibrate_cpu(); printk("Detected %lu.%03lu MHz processor.\n",
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