2017-11-29 17:13 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > On 29/11/2017 09:51, Wanpeng Li wrote: >> 2017-11-29 16:48 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >>> On 29/11/2017 07:07, Wanpeng Li wrote: >>>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>> >>>> 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@xxxxxxxxxx> >>>> Cc: Jim Mattson <jmattson@xxxxxxxxxx> >>>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >>>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >>>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>> >>> The update_debugctlmsr should stay in vmx_vcpu_run so that tracing >>> features work correctly. However, the get_debugctlmsr indeed can be >> >> The tracing can't run except vCPU is schedule out, so why >> update_debugctlmsr should stay in vmx_vcpu_run? > > For example your patch is disabling BTS (branch trace store) after the > first vmexit, isn't it? I see. Thanks for pointing out. :) Regards, Wanpeng Li
