Re: [libvirt] [PATCH 1/8] qemu: bulk stats: extend internal collection API
----- Original Message -----
From: "Peter Krempa" <pkrempa(a)redhat.com>
To: "Francesco Romani" <fromani(a)redhat.com>, libvir-list(a)redhat.com
Sent: Wednesday, September 10, 2014 10:07:33 AM
Subject: Re: [libvirt] [PATCH 1/8] qemu: bulk stats: extend internal collection API
[...]
>> Hmm this skips offline domains entirely if one of the stats
groups needs
>> the monitor.
>>
>> I think we should rather skip individual stats groups, or better stats
>> fields that we can't provide.
>>
>> Any ideas?
>
> What about this (pseudo-C):
>
> unsigned int privflags = 0;
>
> if (needmon && qemuDomainObjBeginJob(driver, dom, QEMU_JOB_QUERY)
> needmon = false;
> /* auto disable monitoring, the remainder of the function should be
> unchanged */
> else
> privflags |= MONITOR_AVAILABLE;
>
> if ((needmon && virDomainObjIsActive(dom)) || !needmon) {
> if (qemuDomainGetStats(conn, dom, stats, &tmp, privflags) < 0)
> /* pass monitor availability down the chain. Individual workers
> will
> bail out immediately and silently if they need monitor but
> it is
> not available
> */
> goto endjob;
>
> if (tmp)
> tmpstats[nstats++] = tmp;
> }
>
>
> No other change should be needed to this patch, and with trivial changes
> all the others can be fixed.
Also you can just grab the lock always and the workers will exit if the
VM is not alive. Having a domain job should be fine.
As you prefer. For oVirt, we do care of all the stats group implemented, and always all of
them,
(actually I may have missed some bits, e.g. the pininfo as you pointed out elsewhere -
going to fix),
so for our needs we'll always need to enter the monitor.
But other users of this API may beg to differ, and I believe is fair to assume that other
consumers
of this API could just use stats which doesn't require to enter the monitor: e.g.
CPU/VCPU/interface.
Hence, I was trying to be a good citizen and do not require monitor access unless it is
actually
needed; but if turns out it is OK to do a domain job anyway, I'll happily simplify my
code :)
Thanks and bests,
--
Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani