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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id p12sm22637661eds.39.2021.01.05.05.06.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jan 2021 05:06:09 -0800 (PST) From: Vitaly Kuznetsov To: Alexey Makhalov Cc: linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hpa@zytor.com, bp@alien8.de, mingo@redhat.com, tglx@linutronix.de, pv-drivers@vmware.com, sdeep@vmware.com Subject: Re: [PATCH] x86/vmware: avoid TSC recalibration In-Reply-To: <20210105004752.131069-1-amakhalov@vmware.com> References: <20210105004752.131069-1-amakhalov@vmware.com> Date: Tue, 05 Jan 2021 14:06:08 +0100 Message-ID: <87im8bildr.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alexey Makhalov writes: > When TSC frequency is known (retrieved from hypervisor), we should skip > TSC refined calibration by setting X86_FEATURE_TSC_KNOWN_FREQ. > > Signed-off-by: Alexey Makhalov > --- > arch/x86/kernel/cpu/vmware.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c > index c6ede3b3d302..83164110ccc5 100644 > --- a/arch/x86/kernel/cpu/vmware.c > +++ b/arch/x86/kernel/cpu/vmware.c > @@ -378,6 +378,8 @@ static void __init vmware_set_capabilities(void) > { > setup_force_cpu_cap(X86_FEATURE_CONSTANT_TSC); > setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE); > + if (vmware_tsc_khz) > + setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ); > if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMCALL) > setup_force_cpu_cap(X86_FEATURE_VMCALL); > else if (vmware_hypercall_mode == CPUID_VMWARE_FEATURES_ECX_VMMCALL) The same trick is being used in Xen/Jailhouse/KVM code already and Hyper-V overwrites x86_platform.calibrate_tsc/x86_platform.calibrate_cpu hooks to basically achive the same goal. Should we maybe introduce a flag in 'struct hypervisor_x86' or something like that to unify all this? Just a suggestion. -- Vitaly