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Date: Tue, 5 Dec 2017 16:15:23 -0800 From: Nadav Amit <nadav.amit@...il.com> To: Radim Krčmář <rkrcmar@...hat.com> Cc: Wanpeng Li <kernellwp@...il.com>, LKML <linux-kernel@...r.kernel.org>, kvm list <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>, Wanpeng Li <wanpeng.li@...mail.com>, Jim Mattson <jmattson@...gle.com> Subject: Re: [PATCH v2] KVM: VMX: Cache IA32_DEBUGCTL in memory Radim Krčmář <rkrcmar@...hat.com> wrote: > 2017-11-29 01:31-0800, Wanpeng Li: >> From: Wanpeng Li <wanpeng.li@...mail.com> >> >> MSR_IA32_DEBUGCTLMSR is zeroed on VMEXIT, so it is saved/restored >> each time during world switch. Jim from Google pointed out that >> when running schbench in L2, vmx_vcpu_run will occupy 4% cpu time, >> and the 25% of vmx_vcpu_run cpu time is occupied by get_debugctlmsr(). >> This patch caches the host IA32_DEBUGCTL MSR and saves/restores >> the host IA32_DEBUGCTL msr when guest/host switches to avoid to >> save/restore each time during world switch. >> >> Suggested-by: Jim Mattson <jmattson@...gle.com> >> Cc: Paolo Bonzini <pbonzini@...hat.com> >> Cc: Radim Krčmář <rkrcmar@...hat.com> >> Cc: Jim Mattson <jmattson@...gle.com> >> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com> >> --- > > Queued, thanks. > > And there is another optimization loosely connected to the "[PATCH v3 > 00/16] Move vcpu_load and vcpu_put calls to arch code" series: > We only need to read the value for the KVM_RUN ioctl. Can you add some warning that would fire in some “debug” mode if the cached value is not identical to the real one? Thanks, Nadav
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