From: Peter Zijlstra <peterz@infradead.org>
To: zhenwei pi <pizhenwei@bytedance.com>
Cc: tglx@linutronix.de, pbonzini@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: Re: [PATCH v2 1/2] x86/cpu: Introduce x86_get_cpufreq_khz()
Date: Sat, 4 Dec 2021 11:46:00 +0100 [thread overview]
Message-ID: <20211204104600.GT16608@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <947de021-df91-9219-7378-8addc6f66612@bytedance.com>
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.
next prev parent reply other threads:[~2021-12-04 10:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-01 2:46 [PATCH v2 0/2] Introduce x86_get_cpufreq_khz() zhenwei pi
2021-12-01 2:46 ` [PATCH v2 1/2] x86/cpu: " zhenwei pi
2021-12-02 22:25 ` Peter Zijlstra
2021-12-03 7:34 ` zhenwei pi
2021-12-04 10:46 ` Peter Zijlstra [this message]
2021-12-01 2:46 ` [PATCH v2 2/2] KVM: x86: use x86_get_freq to get freq for kvmclock zhenwei pi
2021-12-02 2:48 ` Thomas Gleixner
2021-12-02 5:26 ` zhenwei pi
2021-12-02 7:19 ` Maxim Levitsky
2021-12-02 22:45 ` Peter Zijlstra
2021-12-03 7:53 ` Maxim Levitsky
2021-12-04 10:44 ` Peter Zijlstra
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