Re: [libvirt] [RFC][scale] new API for querying domains stats
----- Original Message -----
From: "Francesco Romani" <fromani(a)redhat.com>
To: libvir-list(a)redhat.com
Sent: Friday, July 4, 2014 6:44:07 PM
Subject: Re: [libvirt] [RFC][scale] new API for querying domains stats
> > However, a question here about bulk APIs.
> > One cornerstone of oVirt is shared storage (NFS, ISCSI...); another is
> > qemu/kvm,
> > and COW images are supported (probably even the default, need to check).
> >
> > Due to storage being unavailable because a network outage, it happened
> > that
> > virDomainGetBlockInfo blocked beyond recover.
> >
> > On such scenarios, how will a bulk API behave? There will be a timeout or
> > something else?
>
> It depends on the storage and the way it is configured. If NFS is mounted
> with 'hard' + 'nointr' any call libvirt makes to dead storage will
get
> stuck in an uninterruptable sleep in kernel space. There's no way for
> libvirt to time out since by the very definition of 'hard' mount option
> it does not time out. If you mount with 'soft' then the calls libvirt
> makes will time out.
My bad, I worded poorly my question.
What I mean is: on top of what the kernel or QEMU (libnfs, libiscsi) does,
there are plans for any additional mechanism/safeguard?
(I guess no, I'm asking just to be sure).
Hi,
maybe borderline offtopic, but still about blocking calls:
We (VDSM/oVirt developers) are reviewing our usage of libvirt in sampling.
Afer a (quick) inspection of the code, I believe the following calls cannot
block due to FS/storage issues, as they do not need it in any way
I'm quite confident about these
* virDomainGetCPUStats: uses cgroups only (no FS/storage access)
* virDomainInterfaceStats: uses /proc/net/dev (no FS/storage access)
* virDomainGetVcpus: uses uses /proc and syscall for PCPU affinity (no FS/storage access)
* virDomainSchedulerParameters: which uses cgroups (no FS/storage access)
Not sure about this, but it looks to me they don't need to access FS/storage either:
* virDomainGetVcpusFlags
* virDomainGetMetadata
Can please anyone confirm or deny?
Thanks and best regards
--
Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani