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? Thanks, Paolo
