[ovirt-users] Guest VM Running 160 RCU Processes

[Darrell Budic]

> On Oct 22, 2014, at 6:43 AM, Michal Skrivanek <michal.skrivanek at redhat.com> wrote:
> 
> On Oct 21, 2014, at 18:13 , Darrell Budic <budic at onholyground.com> wrote:
> 
>> Was poking at this a little to see if there was any tuning that could affect it and spotted some oddness with the processor counts on my VMs under Ovirt 3.4. They seem to think they only have the proper number I set in ovirt (as shown in /proc/cpu), but if I look at dmidecode, there’s 159 bogus processors listed. I’d expect maybe 16 from the -smp 1,maxcpus=16,sockets=16,cores=1,threads=1 argument to qemu-kvm, but there are 0xa0 of them. Maybe this is a seabios or qemu-kvm issue causing all those extras? Anyway, the # of rcu* processes matches pretty well, so that’s likely where it’s coming from.
>> 
>> At least they shouldn’t be causing a performance issue, given their purpose as non-blocking work threads, but it is odd to see.
>> 
>> Punit, did you open a BZ I can add these details to?
>> 
>> BTW, this appears to be corrected with some component of Ovirt 3.5 (probably qemu-rhev?). On VMs started after I upgraded my Engine (even on 3.4 vdsmds), I’m only seeing 16 “processors” in the bios, and thus only 16 of the various rcu* processes. Could have been a general Centos 6.5 update too, since I did those as well, so I can’t get any finer resolution on that issue (both engine and host nodes, lots of Centos 7 VMs).
>> 
>> If there is a RFE for this, perhaps a configurable max # of CPU sockets for hot add could be added, or it could be limited to the max physical cpu count of the biggest host in the cluster?
> 
> The max is 16. Roy, what can we change/not change after your latest changes?
> I suppose it's related to teh maximum values we send because of hotplug support
> 
> Thanks,
> michal

Yes, definitely looks like a side effect of hot plug. The 160 rcu issues look like a bug somewhere else, 16 is more normal for the default. I had missed the engine setting for MaxNumOfVmCpus, I’ll probably set that for my smaller hosts just to keep it reasonable for the hardware it’s on.

> From: "Punit Dambiwal" <hypunit at gmail.com>
> To: "Doron Fediuck" <dfediuck at redhat.com>
> Sent: Wednesday, October 22, 2014 4:19:56 AM
> Subject: Re: [ovirt-users] Guest VM Running 160 RCU Processes
> 
> Hi Darrell,
> 
> I haven't open a BZ for the same...please let me know how i can open BZ ??

Punit, make sure your replies go to the list, this didn’t get to me. But you want to go to http://www.ovirt.org/Community and look at the “Find and File Bugs” section to raise a bug or file an RFE.

  -Darrell