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

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Message-ID: <20160916105905.2fb512b9@redhat.com>
Date:   Fri, 16 Sep 2016 10:59:05 -0400
From:   Luiz Capitulino <lcapitulino@...hat.com>
To:     Paolo Bonzini <pbonzini@...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 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).

> 
> 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
> >   
>