Re: [PATCH] kvm/stats: Update kvm stats to clear on write to their debugfs entry

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Mon, 2016-10-17 at 15:48 +0200, Christian Borntraeger wrote:
> On 10/17/2016 03:40 PM, Radim Krčmář wrote:
> > 
> > 2016-10-14 17:02+1100, Suraj Jitindar Singh:
> > > 
> > > Various kvm vm and vcpu stats are provided via debugfs entries.
> > > Currently there is no way to reset these stats back to zero for
> > > the system
> > > except by stopping all vms.
> > It is not really resetting, just a special case of current behavior
> > --
> > top-level stats are a sum of all existing VMs/VCPUs, so we would
> > see 0
> > if they all had 0.
> > 
> > > 
> > > Add the ability to clear (reset back to zero) these stats on a
> > > per stat
> > > basis by writing to the debugfs files.
> > I can see this being used before a test, but the userspace could
> > also
> > read the value instead of writing and subtract it from the value
> > after
> > the test to get a similar result.
> > 
> > The userspace-only solution is insufficient?
> > 
> > When and what do you zero?
> > 
> > > 
> > >                                        The stats are just reset
> > > to zero
> > > irrespective of what is actually written to the file.
> > Sounds good.  Setting the val would be as simple, but there
> > shouldn't be
> > a reason to and it is a debug interface, so we can change it
> > anytime.
> > 
> > > 
> > > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> > > ---
> > I have applied it to kvm/queue for the moment, thanks.
> FWIW, I was thinking about another change: provide the accumulated
> values of 
> the counters of all VMs that have been destroyed (basically on
> vm_destroy read
> the values and add them on top of the "forever" counters.
> Did not find the time to do something like this.
This doesn't seem like it would be particularly hard to implement, I'm
just not sure of the use case.
> 
> 
>