On 2012-10-03 08:58, Michael Tokarev wrote: > On 02.10.2012 11:46, Markus Armbruster wrote: >> "Daniel P. Berrange" <berrange@xxxxxxxxxx> writes: > >>> IMHO, default to KVM, fallback to TCG is the most friendly default >>> behaviour. >> >> Friendly perhaps, generating an infinite series of questions "why is my >> guest slow as molasses?" certainly. > > With a warning about "switching to slow emulation mode because .." > printed at startup that becomes a non-issue, because there's no > reason to ask more questions about why it is slow - it already > said why. Yes some may try to ask what to do, which is different. > > Every howto nowadays mentions kvm modules and /dev/kvm device > permissions. > >> And for each instance of the question, there's an unknown number of >> users who give QEMU a quick try, screw up KVM unknowingly, observe the >> glacial speed, and conclude it's crap. > > This is, again, I think, unfair. With the warning message it becomes > more or less obvious. > > If you're talking about users who run it with -daemonize argument - > this is a) stupid to do when TRYING it out, so it's not a big deal > to lose another stupid user, and b) qemu should init everything > first and throw all warnings and fatal errors before daemonizing, > if this is not the case it should be fixed in the code. > > And if you're talking about management software (libvirt and others), > it controls all the required privileges already and explicitly > requests acceleration and other stuff. > > So the best thing to do is what Daniel, Aurelien, Paolo and others > are suggested: accel=kvm:tcg with a warning. Well, we had a lot of problems with such a fallback in the past, but I think we had no proper warnings back then. I'm not fully believing in users will always realize the console message. I would therefore suggest to change the window title of QEMU as well if we fail to initialize some accelerator. Something like "QEMU without KVM" (could be "QEMU without $FAILED_ACCEL" in the end, i.e. not just for KVM). If that makes sense for everyone, I'll hack the required patches. Jan
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