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

[Hemant Kumar]

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 <address@hidden>
> > Signed-off-by: Hemant Kumar <address@hidden>
> > ---
> >   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 <address@hidden>

Thanks!

--
Hemant Kumar