linux-kernel - Re: [PATCH v2 0/6] kvm: x86: export TSC information to user-space

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Date:   Fri, 16 Sep 2016 16:59:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Luiz Capitulino <lcapitulino@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rkrcmar@...hat.com, rostedt@...dmis.org, mhiramat@...nel.org,
        mtosatti@...hat.com
Subject: Re: [PATCH v2 0/6] kvm: x86: export TSC information to user-space



On 16/09/2016 16:59, Luiz Capitulino wrote:
> On Fri, 16 Sep 2016 16:56:34 +0200
> Paolo Bonzini <pbonzini@...hat.com> wrote:
> 
>> On 16/09/2016 16:27, Luiz Capitulino wrote:
>>> [Introduction will follow]
>>>
>>> Changelog
>>> ---------
>>>
>>> v2
>>>
>>>  - add tsc_offset field to struct kvm_vcpu_arch
>>>  - drop read_tsc_offset()
>>>  - add per-vcpu dir entries in debugfs
>>>  - export TSC scaling info (besides TSC offset)
>>>  - export the TSC offset as a signed number
>>>  - drop patch that wrongly tried to improve error
>>>    handling in kvm_create_vm_debugfs()  
>>
>> I've tested this patch on an AMD machine with TSC scaling, so I'm
>> pushing it shortly to kvm/queue.
> 
> Thanks for the testing! Btw, I don't mind letting it sit on the
> list for a few days for review (well, no submitter should mind
> this).

That's what kvm/queue is for. :)

Paolo

>>
>> Paolo
>>
>>> Intro
>>> -----
>>>
>>> This series exports a VM's TSC offset and TSC scaling
>>> information to user-space via a new per-vcpu directory
>>> in debugfs. For example:
>>>
>>>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-offset
>>>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio
>>>   /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio-frac-bits
>>>
>>> The TSC offset in particular is needed in user-space
>>> in order for tracing tools, such as trace-cmd, to be
>>> able to merge the host and guest traces using the
>>> host TSC. This is explained in detail in this thread:
>>>
>>>   [Qemu-devel] [RFC] host and guest kernel trace merging
>>>   https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html
>>>
>>> Luiz Capitulino (6):
>>>   kvm: x86: add tsc_offset field to struct kvm_vcpu_arch
>>>   kvm: x86: drop read_tsc_offset()
>>>   kvm: kvm_destroy_vm_debugfs(): check debugfs_stat_data pointer
>>>   kvm: add stubs for arch specific debugfs support
>>>   kvm: create per-vcpu dirs in debugfs
>>>   kvm: x86: export TSC information to user-space
>>>
>>>  arch/arm/kvm/arm.c              | 10 ++++++
>>>  arch/mips/kvm/mips.c            | 10 ++++++
>>>  arch/powerpc/kvm/powerpc.c      | 10 ++++++
>>>  arch/s390/kvm/kvm-s390.c        | 10 ++++++
>>>  arch/x86/include/asm/kvm_host.h |  2 +-
>>>  arch/x86/kvm/Makefile           |  2 +-
>>>  arch/x86/kvm/debugfs.c          | 69 +++++++++++++++++++++++++++++++++++++++++
>>>  arch/x86/kvm/svm.c              |  8 -----
>>>  arch/x86/kvm/vmx.c              |  6 ----
>>>  arch/x86/kvm/x86.c              | 12 +++++--
>>>  include/linux/kvm_host.h        |  4 +++
>>>  virt/kvm/kvm_main.c             | 40 ++++++++++++++++++++++--
>>>  12 files changed, 161 insertions(+), 22 deletions(-)
>>>  create mode 100644 arch/x86/kvm/debugfs.c
>>>   
>>
>