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Bug 1066209

Summary: Libvirt should calculate and pass vectors parameter to qemu command line for multiqueue virtio device
Product: Red Hat Enterprise Linux 7 Reporter: jason wang <jasowang>
Component: libvirtAssignee: Michal Privoznik <mprivozn>
Status: CLOSED CURRENTRELEASE QA Contact: Virtualization Bugs <virt-bugs>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.0CC: acathrow, bili, chhu, dyuan, honzhang, juzhang, lcui, mprivozn, mzhan, narendra_k, zhwang
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: libvirt-1.1.1-24.el7 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 1071888 (view as bug list) Environment:
Last Closed: 2014-06-13 09:19:11 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1071888    

Description jason wang 2014-02-18 03:09:06 UTC 
Description of problem:

Libvirt should calculate the number of msix vectors and pass it to qemu command line for multiqueue virtio-net (maybe scsi). Otherwise the all virtqueue will share a single vector which will damage the performance.

Upstream commit:

commit 4f588a1b465e2b32c78429e8d2f2c010eb11da19
Author:     Michal Privoznik <mprivozn>
AuthorDate: Fri Aug 23 09:48:24 2013 +0200
Commit:     Michal Privoznik <mprivozn>
CommitDate: Thu Jan 9 15:23:57 2014 +0100

    qemuBuildNicDevStr: Set vectors= on Multiqueue
    
    Yet another advice appeared on the Multiqueue wiki page:
    
    http://www.linux-kvm.org/page/Multiqueue#Enable_MQ_feature
    
    We should add vectors=N onto the qemu command line, where
    N = 2 * (number of queues) + 1.

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.
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Actual results:


Expected results:


Additional info:
Comment 2 Michal Privoznik 2014-02-18 11:00:53 UTC 
Moving to POST:

http://post-office.corp.redhat.com/archives/rhvirt-patches/2014-February/msg00467.html

Moreover, I've build a scratch build to test:

https://brewweb.devel.redhat.com/taskinfo?taskID=7073866
Comment 3 hyao@redhat.com 2014-02-20 07:54:12 UTC 
Reproduced the bug with 
#rpm -qa libvirt
libvirt-1.1.1-23.el7.x86_64
1. Add the following config in domain xml. 
<interface type='network'>
      <mac address='52:54:00:92:d5:ba'/>
      <source network='default'/>
      <target dev='vnet2'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </interface>
2.Start the guest and check the qemu command, vectors=2N+1 is not added. 
#ps aux | grep qemu | grep virtio-net



Test the bug with scratch build: 
#rpm -qa libvirt
libvirt-1.1.1-23.el7multiqueue.x86_64

1. Add the following config in domain xml. 
<interface type='network'>
      <mac address='52:54:00:92:d5:ba'/>
      <source network='default'/>
      <target dev='vnet2'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/>
      <alias name='net1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </interface>
2.Start the guest and check the qemu command, vectors=2N+1 is added. 
#ps aux | grep qemu | grep virtio-net
...-device virtio-net-pci,tx=bh,ioeventfd=on,event_idx=off,mq=on,vectors=11,netdev=hostnet1,id=net1,mac=52:54:00:92:d5:ba,bus=pci.0,addr=0x6 ...
Comment 5 EricLee 2014-02-26 08:34:26 UTC 
Verified pass on libvirt-1.1.1-24.el7, steps as comment #3.
Comment 6 Ludek Smid 2014-06-13 09:19:11 UTC 
This request was resolved in Red Hat Enterprise Linux 7.0.

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