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[Qemu-devel] [Bug 1470720] Re: high IRQ-TLB generates network interrupti

From: Robert van Leeuwen
Subject: [Qemu-devel] [Bug 1470720] Re: high IRQ-TLB generates network interruptions
Date: Mon, 08 Aug 2016 07:01:49 -0000

Disabling huge pages seem to help.
Strangely this should theoretically increase the issue but it so far we have 
not seen issues after disabling THP.
(have not seen high load spikes in a week but this might also be holiday 

So other people can try it out:
echo never >/sys/kernel/mm/transparent_hugepage/defrag
echo never > /sys/kernel/mm/transparent_hugepage/enabled

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  high IRQ-TLB generates network interruptions

Status in QEMU:

Bug description:
   we are having a problem in our hosts, all the vm running on them
  suddenly, and for some seconds, lost network connectivity.

  the root cause appears to be the increase of irb-tlb from low values
  (less than 20) to more than >100k, that spike only last for some
  seconds then everything goes back to normal

  i've upload an screenshot of collectd for one hypervisor here

  we have hosts running precise (qemu 1.5, ovs 2.0.2, libvirt 1.2.2 and kernel 
3.13) where the issue is frequent. also we have an small % of our fleet running 
trusty (qemu 2.0.0 ovs 2.0.2 libvirt 1.2.2 and kernel 3.16) where the problem 
seemed to be nonexistent until today

  issue seems to be isolated to < 10% of our hypervisors, some hypervisors had 
this problem every few days, others only once or twice. our vm are a black box 
to us we don't know what users run on them, but mostly cpu and network bound 
  most of our guests run centos 6.5 (kernel 2.6.32)

  vm are bridged to a linuxbridge then veth wired to an ovs switch
  (neutron openvswitch agent setup)

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