lkml.org 
[lkml]   [2017]   [Nov]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] KVM: VMX: Cache IA32_DEBUGCTL in memory
From
Date
On 29/11/2017 09:51, Wanpeng Li wrote:
> 2017-11-29 16:48 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>> On 29/11/2017 07:07, Wanpeng Li wrote:
>>> From: Wanpeng Li <wanpeng.li@hotmail.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@google.com>
>>> Cc: Jim Mattson <jmattson@google.com>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>>
>> 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

\
 
 \ /
  Last update: 2017-11-29 10:14    [W:2.039 / U:1.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site