lkml.org 
[lkml]   [2021]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Re: [PATCH v2 1/2] x86/cpu: Introduce x86_get_cpufreq_khz()
On Fri, Dec 03, 2021 at 03:34:04PM +0800, zhenwei pi wrote:
> A KVM guest overwrites the '.calibrate_tsc' and '.calibrate_cpu' if kvmclock
> is supported:
>
> in function kvmclock_init(void) (linux/arch/x86/kernel/kvmclock.c)
> ...
> x86_platform.calibrate_tsc = kvm_get_tsc_khz;
> x86_platform.calibrate_cpu = kvm_get_tsc_khz;
> ...
>
> And kvm_get_tsc_khz reads PV data from host side. Before guest reads this,
> KVM should writes the frequency into the PV data structure.
>
> And the problem is that KVM gets tsc_khz directly without aperf/mperf
> detection. So user may gets different frequency(cat /proc/cpuinfo) from
> guest & host.
>
> Or is that possible to export function 'aperfmperf_get_khz'?

TSC frequency and aperf/mperf are unrelated. You're trying to make apple
juice with carrots.

\
 
 \ /
  Last update: 2021-12-04 11:47    [W:0.064 / U:5.864 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site