Re: [PATCH] KVM: Create debugfs statistics for each VM

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 02/05/2016 10:02 AM, Janosch Frank wrote:
> On 02/04/2016 02:10 PM, Christian Borntraeger wrote:
>> On 02/04/2016 02:05 PM, Paolo Bonzini wrote:
>>>
>>>
>>> On 02/02/2016 15:14, Christian Borntraeger wrote:
>>>> FWIW, the newly created subfolders,
>>>>
>>>> require QEMU commit 6590045e5dd2fb0b1d7cdc047ae0c52fd4bb5276
>>>>     scripts/kvm/kvm_stat: Replaced os.listdir with os.walk
>>>>
>>>> Otherwise you might get errors like 
>>>>
>>>> Traceback (most recent call last):
>>>>   File "scripts/kvm/kvm_stat", line 640, in <module>
>>>>     curses.wrapper(tui, stats)
>>>>   File "/usr/lib64/python2.7/curses/wrapper.py", line 43, in wrapper
>>>>     return func(stdscr, *args, **kwds)
>>>>   File "scripts/kvm/kvm_stat", line 547, in tui
>>>>     refresh(sleeptime)
>>>>   File "scripts/kvm/kvm_stat", line 523, in refresh
>>>>     s = stats.get()
>>>>   File "scripts/kvm/kvm_stat", line 483, in get
>>>>     new = d.read()
>>>>   File "scripts/kvm/kvm_stat", line 37, in read
>>>>     return dict([(key, val(key)) for key in self._fields])
>>>>   File "scripts/kvm/kvm_stat", line 36, in val
>>>>     return int(file(self.base + '/' + key).read())
>>>> IOError: [Errno 21] Is a directory: '/sys/kernel/debug/kvm/13123-31'
>>>>
>>>> when using the "-d" option.
>>>>
>>>>
>>>> Paolo, I still think that this a valuable addon for debugging. Any guidance?
>>>
>>> Yeah, I agree...  Do we want to add a module parameter for this, and/or
>>> a kernel configuration that for now defaults to N?

Hmm, a new Kconfig might also be a good idea. 
There is another problem that kvm_stat wants to have /sys/kernel/debug/tracing,
which is only available with CONFIG_TRACING. CONFIG_TRACING cannot be selected by
itself, so you have to enable some other tracer (like function tracing) that
has nothing to do with KVM, which then selects GENERIC_TRACER which selects
CONFIG_TRACING and then enables the kvm trace points.

So maybe a 
config KVM_PER_GUEST_TRACING
that selects GENERIC_TRACER and enables that feature?


>>>
>>
>>
>>> An alternative is to move kvm_stat from QEMU to tools/.
>>
>> Hmm, that is probably the best solution, given that it has no dependency
>> on QEMU but heavily depends on the kernel module.
> 
> So, what's the plan then?
> 
> Give me some pointers and I'm happy to do the work, but I currently
> don't have enough experience to know/guess what is wanted.
> 
> I still have about 3 or 4 patches for kvm_stat in my queue that will add
> the filtering support for debugfs AND tracefs. One of them also adds
> documentation to the script, as well as to the man page and I might add
> one that brings py3 support.
> Most of them are ready, but before finishing the filtering support I
> wanted to wait until the kernel patch was in next.
> 
> Do you (Paolo) want to move this patch through kvm-next and the
> corresponding python patches through qemu and later on move the script
> to the kernel?