Matthew Hall wrote: > Hi Avi, > > I spoke to you a while ago on #kvm on freenode - I had a problem with > ide ops on an amd svm host with kvm. The issues regarded the inability > to access ida devices (hda/hdc) under qemu & kvm on my host - if this > triggers your memory... > > The last point I got to was that it was kvm and amd specific. Id est, > the same image run under an intel vmx host with the *exact* same image, > kvm version and command options (svn 'trunk' from the $date). > The issue seemed to be AMD and kvm specific (running with '-no-kvm' made > everything work ok, but slower, as you'd expect). > > I got word of a possible workaround, from one of your colleagues whilst > you've been away, to use the boot options 'noapic nolapic' on the host > o/s. Using these options solved my hd* op problems and I can boot ok now. >
I've seen a very similar problem on an IBM x460. The main symptom I see is lost timer interrupts in the host. I haven't spent much time looking into this but I suspect it's almost certainly related to the fact that KVM is using a different interrupt delivery method than Xen. Xen doesn't seem to have an issue on this system. I suspect that the interrupts being received that's causing a VMEXIT is not actually getting propagated to the host (the timer being the most frequent interrupt to cause a VMEXIT). If we switch to not to acknowledging the interrupt before the VMEXIT and then regenerating it either with a software interrupt or delivering it directly in the host, it's possible this problem may go away. This is all just speculation though. regards, Anthony Liguori > It seems disabling the local apic was the fundamental part (iirc), as > without host support the guest would always start the dummy apic; so > running the guest with any 'special' options (ie. '-no-apic') should not > be required. > > I'm think this problem is specific to my particular cpu/motherboard > combination aswell. > I also have box with a recent intel cpu (with the vmx extention) which > doesn't display this behaviour; and from talking with you it's not > purely amd specific (I believe your tests on amd cpu worked). > Is it possible a slowdown in the interrupt controller between the guest > and host is a contributing factor? > Iirc, with a 'dummy' apic, I experience a ~5% slowdown on disk and > network operations, which isn't so bad. I've yet to think about smp usage. > > Thought you might appreciate this info should you feel it deserve a wiki > entry. Point me in the direction of the appropriate page should you feel > I can put this info in myself. > > > Best regards, > Matt > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > kvm-devel mailing list > kvm-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/kvm-devel > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
