Re: [Qemu-devel] [PATCH][RESEND] qemu/kvm_stat: Fix I/O error from kvm_stat

[Hemant Kumar <hemant@linux.vnet.ibm.com>]

Hi Wei,

Thanks for the review.

On 09/01/2015 01:52 AM, Wei Huang wrote:
> On 08/30/2015 10:42 PM, Hemant Kumar wrote:
>> Running kvm_stat on a powerpc macine where the kernel is compiled with
>> KVM_BOOK3S_HV_EXIT_TIMING config option, generates the following error :
>>
>>   # kvm_stat
>>
>> Traceback (most recent call last):
>>    File "/usr/bin/kvm_stat", line 644, in <module>
>>      curses.wrapper(tui, stats)
>>    File "/usr/lib64/python2.7/curses/wrapper.py", line 43, in wrapper
>>      return func(stdscr, *args, **kwds)
>>    File "/usr/bin/kvm_stat", line 550, in tui
>>      refresh(sleeptime)
>>    File "/usr/bin/kvm_stat", line 526, in refresh
>>      s = stats.get()
>>    File "/usr/bin/kvm_stat", line 486, in get
>>      new = d.read()
>>    File "/usr/bin/kvm_stat", line 29, in read
>>      return dict([(key, val(key)) for key in self._fields])
>>    File "/usr/bin/kvm_stat", line 28, in val
>>      return int(file(self.base + '/' + key).read())
>> IOError: [Errno 21] Is a directory: '/sys/kernel/debug/kvm/vm12840'
>>
>> The error says that its trying to read the contents of a directory as if
>> it were a file. The kernel here creates directories inside
>> "/sys/kernel/debug/kvm/" for the individual VMs running on the
>> machine. These directories contain timing information (for rm_entry,
>> rm_intr, rm_exit, guest, cede) related to each vcpu of each VM. All of
>> this is enabled with KVM_BOOK3S_HV_EXIT_TIMING config option for the
>> kernel.
> A suggestion: would it be useful to display these statistics in
> perf_stat? I understand that these counters are per-vm-based; but they
> might provide useful insights to end-users.

It would be definitely useful to display these statistics, but since this
script doesn't work on powerpc with the config option enabled, this
patch should work as a fix for now.

We can work on enhancing kvm_stat to display these per vm statistics.

>> kvm_stat script isn't supposed to parse/read these directories and isn't
>> even expecting any directories inside "/sys/kernel/debug/kvm/". This
>> patch fixes the problem by avoiding lookup for these directories.
>>
>> Reported-by: Krishnaja Balachandran <kribalac@in.ibm.com>
>> Signed-off-by: Hemant Kumar <hemant@linux.vnet.ibm.com>
>> ---
>>   scripts/kvm/kvm_stat | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
>> index 7e5d256..1da7a53 100755
>> --- a/scripts/kvm/kvm_stat
>> +++ b/scripts/kvm/kvm_stat
>> @@ -18,7 +18,11 @@ from ctypes import *
>>   class DebugfsProvider(object):
>>       def __init__(self):
>>           self.base = '/sys/kernel/debug/kvm'
>> -        self._fields = os.listdir(self.base)
>> +        files = os.listdir(self.base)
>> +        self._fields = []
>> +        for f in files:
>> +            if os.path.isfile(self.base + '/' + f):
>> +                self._fields.append(f)
>>       def fields(self):
>>           return self._fields
>>       def select(self, fields):
>>
> I tested this patch on x86 box and didn't see any problem. So:
>
> Reviewed-by: Wei Huang <wei@redhat.com>

Thanks!

-- 
Hemant Kumar