答复: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers

From: "Li,Rongqing" <lirongqing@baidu.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>, "bp@alien8.de" <bp@alien8.de>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"joro@8bytes.org" <joro@8bytes.org>,
	"jmattson@google.com" <jmattson@google.com>,
	"wanpengli@tencent.com" <wanpengli@tencent.com>,
	"vkuznets@redhat.com" <vkuznets@redhat.com>,
	"sean.j.christopherson@intel.com"
	<sean.j.christopherson@intel.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>
Subject: 答复: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers
Date: Sun, 26 Apr 2020 08:30:26 +0000	[thread overview]
Message-ID: <4fecc02b00f6469e81ffc40de4f7188c@baidu.com> (raw)
In-Reply-To: <20200424100143.GZ20730@hirez.programming.kicks-ass.net>

> 
> But then here you only emulate it for VMX, which then results in SVM guests
> going wobbly.
> 
> Also, on Intel, the moment you advertise APERFMPERF, we'll try and read
> MSR_PLATFORM_INFO / MSR_TURBO_RATIO_LIMIT*, I don't suppose you're
> passing those through as well?
> 

init_freq_invariance(void) is trying read MSR_PLATFORM_INFO / MSR_TURBO_RATIO_LIMIT*,
should we add a check of turbo status in init_freq_invariance, to avoid the reading?

It is unnecessary to call intel_set_max_freq_ratio  If turbo is disabled

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fe3ab9632f3b..54fb88323293 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2009,6 +2009,9 @@ static void init_freq_invariance(void)
        if (smp_processor_id() != 0 || !boot_cpu_has(X86_FEATURE_APERFMPERF))
                return;
 
+       if (turbo_disabled())
+               return;
+
        if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL)
                ret = intel_set_max_freq_ratio();

-Li
