Hi, After booting a recently-installed Centos 5.5 i686 guest (with no additional packages), qemu-kvm hogs the host's cpu. Inside the guest, there's no CPU activity. If I disable APIC in the guest, this does not happen. Thanks, Alex
tags 604240 + unreproducible moreinfo thanks 21.11.2010 14:25, Alex wrote: I can't reproduce this in my test install. I bothered to d/load centOS 5.5 cd and installed it in kvm - it works correctly. So you'll need to provide information about how to reproduce this problem. Especially the kvm command line you're using, your host (32 or 64 bits), actual way how you installed centOS. One of the possibilities is actually some bug in CentoOS (RedHat) kernel - their kernel is too old and too messy. I'm afraid even if I'll be able to reproduce the issue, I'll have to close this bugreport (or tag it with 'wontfix') -- the mess they do in RH kernels is basically unrepairable. /mjt
OK, no worries. My QEMU commandline is: /usr/bin/kvm -S -M pc-0.12 -cpu qemu32 -enable-kvm -m 512 -smp 1,sockets=1,cores=1,threads=1 -name noctem -uuid 1bccb2d6-edbc-3831-7190-39a8b5c34b4a -nodefaults -chardev socket,id=monitor,path=/var/lib/libvirt/qemu/noctem.monitor,server,nowait -mon chardev=monitor,mode=readline -rtc base=utc -boot c -drive file=/var/lib/libvirt/images/noctem.img,if=none,id=drive-virtio-disk0,boot=on,format=raw -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 -drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:87:1a:e1,bus=pci.0,addr=0x3 -net tap,fd=59,vlan=0,name=hostnet0 -chardev pty,id=serial0 -device isa-serial,chardev=serial0 -usb -vnc 127.0.0.1:0 -vga cirrus -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 My installation of CentOS was quite standard, I unselected the Gnome Desktop task selection (so I installed the bare install). My host is: # uname -a Linux case 2.6.32-4-amd64 #1 SMP Tue Apr 6 08:21:34 UTC 2010 x86_64 GNU/Linux userland is 32 bits, although I'm not sure why that does not show in uname. I have a workaround for the bug (disabling APIC), so if the bug has to be closed that's OK for me (and this bug will show up in Google if someone stumbles across the same problem). Thanks for your time, Àlex
tags 604240 - moreinfo unreproducible tags 604240 + confirmed severity 604240 wishlist retitle 604240 Centos 5.5 guest hogs CPU thanks 21.11.2010 15:59, Alex wrote: ... Ok. I was able to trigger this independently - indeed, guest eats CPU on the host. The situation becomes a bit better when booting it with noapic, but it's not a solution unfortunately: it still uses 25..30% host CPU time when idle (not 50% (of two cores) without noapic). I tested qemu-kvm_0.13 too, and it shows the same effect. This is most likely a bug in Redhat kernel. I'll try to check other combinations of 32/64 host/guest if time permits, but don't hold the breath - to me it's of low priority. For now I'll mark it as minor and confirmed. Minor because it works, just uses more CPU time on host than necessary. Also retitling - removing APIC reference, since while noapic helps somwhat, it does not eliminate the issue still. I don't plan to close the bug right away, just because maybe there's something in kvm that can be changed. Thanks!
An update to this bugreport. We tried triggering it on several machines, and discovered the following: The high load on host is due to rhel/centos 5 kernel using 1000Hz timer tick, and their kernel is not tickless. The load will be higher or lower depending on your host cpu speed, cpufreq profile and other factors like that. There's one machine I have, with a CPU similar to your (older Athlon X2, Brisbane and the like, 64nm technology) -- Turion TL-52 (1.6GHz). On this CPU, CentOS behaves very unreliable, -- sometimes it stops (with 100% cpu on host) during boot, sometimes during shutdown, sometimes during regular operations. The key difference (I think) of this machine from all others is that it has unstable tsc, while on all others it's stable. The behavour does not depend much on noapic guest setting, while it seems it occurs a bit less frequently with noapic. Were you able to boot the guest at all, or does it stall on you and does not work? The fact that if behaves badly on non-stable-tsc suggests it's a bug in redhat kernel still - there were a few similar bugs fixed in recent upstream (-stable included) kernels. The same behavour is observed on qemu-kvm 0.12 and 0.13. So I still think its redhat kernel bug, for now - preliminary. Thanks! /mjt
Hi, Yup, I didn't even notice the problem until the CPU fans went into overdrive. Thank you for your time (however, note that this is not critical to me) Cheers, Alex
tags 604240 + wontfix thanks Tagging as wontfix -- this is a problem in old kernels (including those used in rhel/cenos 5.x), nothing qemu/kvm can do about. Thanks, /mjt
tags 604240 + wontfix thanks Tagging as wontfix -- this is a problem in old kernels (including those used in rhel/cenos 5.x), nothing qemu/kvm can do about. Thanks, /mjt