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Bug 1510741 - Invalid warning about number of hotpluggable cpus
Summary: Invalid warning about number of hotpluggable cpus
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: qemu-kvm-rhev
Version: 7.5
Hardware: All
OS: Unspecified
low
low
Target Milestone: rc
: ---
Assignee: Andrew Jones
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On: 1495456
Blocks:
TreeView+ depends on / blocked
 
Reported: 2017-11-08 06:54 UTC by Xujun Ma
Modified: 2017-12-04 12:32 UTC (History)
11 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2017-12-04 12:32:31 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)

Description Xujun Ma 2017-11-08 06:54:28 UTC 
Description of problem:
Invalid warning about number of hotpluggable cpus

Version-Release number of selected component (if applicable):
qemu-kvm-rhev-2.10.0-4.el7.ppc64le

How reproducible:
100%

Steps to Reproduce:
1.Boot up guest with command:
/usr/libexec/qemu-kvm \
 -smp 240,sockets=1,cores=30,threads=8 \
 -m 4096 \
 -nodefaults \
 -device nec-usb-xhci,id=xhci \
 -device usb-tablet,id=tablet \
 -device usb-kbd,id=kbd \
 -device virtio-scsi-pci,bus=pci.0 \
 -device scsi-hd,id=scsi-hd0,drive=scsi-hd0-dr0,bootindex=0 \
 -drive file=rhel75-ppc64le-virtio.qcow2,if=none,id=scsi-hd0-dr0,format=qcow2,cache=none \
 -device virtio-net-pci,netdev=net0,id=nic0,mac=52:54:00:c4:e7:84 \
 -netdev tap,id=net0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown,vhost=on \
 -monitor stdio \

2.
3.

Actual results:
Warning: Number of SMP cpus requested (240) exceeds the recommended cpus supported by KVM (192)
Warning: Number of hotpluggable cpus requested (240) exceeds the recommended cpus supported by KVM (192)
QEMU 2.10.0 monitor - type 'help' for more information
(qemu) VNC server running on ::1:5900


Expected results:
there is no hotpluggable cpus,should remove this warning.it should display when use maxcpus=240.

Additional info:
ppc only
Comment 2 David Gibson 2017-11-09 02:45:17 UTC 
Essentially cosmetic, dropping priority.
Comment 3 David Gibson 2017-12-01 02:47:38 UTC 
So this isn't actually ppc specific.  It's just that the message is more likely to be triggered on ppc, because we have a recommended max vcpu count which depends on the number of host cpus.

Looks like the code in qemu which gives this message comes from Andrew Jones - reassigning to him.
Comment 4 Andrew Jones 2017-12-04 12:32:31 UTC 
(In reply to Xujun Ma from comment #0)
> Actual results:
> Warning: Number of SMP cpus requested (240) exceeds the recommended cpus
> supported by KVM (192)
> Warning: Number of hotpluggable cpus requested (240) exceeds the recommended
> cpus supported by KVM (192)

The above appears to be working as designed.

> 
> Expected results:
> there is no hotpluggable cpus,should remove this warning.it should display
> when use maxcpus=240.

Ah, so the complaint isn't that the 'SMP' warning is issued, or even that the 'hotpluggable' warning should be issued when maxcpus=240, but that the 'hotpluggable' warning is issued when maxcpus isn't specified on the command line. That's an incorrect expectation. The way the -smp command line works is that max_cpus defaults to smp_cpus when it is not provided, e.g. '-smp 240' is equivalent to '-smp 240,maxcpus=240'

Thanks,
drew
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