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Re: [fedora-virt] how can i verify that HW extensions are being used?



On Thu, 16 Apr 2009, Mark McLoughlin wrote:

> On Thu, 2009-04-16 at 07:48 -0400, Robert P. J. Day wrote:
>
> > apparently, i made one lame-brained move yesterday that almost
> > certainly caused my VM to run thigh-suckingly slowly.  following
> > the linux KVM FAQ, i wanted to configure KVM so i could run it as
> > a non-root user.  to that end, i
> >
> >   * created a "kvm" group,
> >   * added my user account to the kvm group, and
> >   * added the rules file /etc/udev/rules.d/60-kvm.rules:
> >
> >     KERNEL=="kvm", GROUP="kvm"
> >
> >   i re-initialized udev with:
> >
> >   # udevadm control --reload-rules   (right?)
> >
> > unloaded my kvm modules (kvm and kvm_amd), reloaded them and, sure
> > enough, my new /dev/kvm device file had a group affiliation of
> > kvm. excellent, i thought, and away i went ... with still
> > painfully slow performance, until i realized that i was still in
> > my original desktop session which *wasn't* considered part of the
> > kvm group.  so a quick logout, log back in and things were much
> > better.
> >
> >   *that's* the sort of thing i'm trying to document as i write all
> > of this up -- those slight oversights which no one bothers to
> > mention that eventually bite you in the butt.
>
> You absolutely should not have needed to do that. We very much want
> this to "just work".
>
> Please give some more details so we can get to the bottom of what
> your problem was.

  actually, this is one case where qemu/kvm appears to have worked
properly, and it was my mistake.  from here:

http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F

you read how to allow kvm usage as a non-root user with udev.  so (and
the following is from memory), first, i created the new group "kvm",
then added my regular user account to that group.  piece of cake.

  next, i added a new udev rules file, 60-kvm.rules, which contained
only:

  KERNEL=="kvm", GROUP="kvm"

unloaded kvm modules, reloaded, but /dev/kvm was still (root, root).
then realized i needed to get udev to reconsult its rules to pick up
that new file, so i ran:

  # udevadm control --reload-rules

unloaded modules, reloaded and /dev/kem was now (root, kvm), as it
should be.

  annoyingly, installing was still screamingly slow until i realized
that i was still logged into my desktop from my user account which did
*not* have kvm groupship (verified that with "id" in an xterm).  so
logged out of X, logged back in as same account, i was now in the
"kvm" group, and things went *much* faster.

  here's the rub -- i think there was a reboot in there somewhere and
i'm not sure if that affected anything.  but if you read that linux
kvm FAQ again:

http://www.linux-kvm.org/page/FAQ#How_can_I_check_that_I.27m_not_falling_back_to_qemu_with_no_hardware_acceleration.3F

In that case, you can check that:

    * the modules are correctly loaded lsmod|grep kvm
    * you don't have a "KVM: disabled by BIOS" line in the output of dmesg
    * /dev/kvm exists and you have the correct rights to use it

that last point seems fairly adamant that your account *needs* access
to /dev/kvm so, if that's true, i *shouldn't* have had HW support
until i did all of the above.  i don't see how you could shortcut any
of the above.  would anyone else like to try it and see if it matches
what happened to me?

rday
--

========================================================================
Robert P. J. Day                               Waterloo, Ontario, CANADA

        Linux Consulting, Training and Annoying Kernel Pedantry.

Web page:                                          http://crashcourse.ca
Linked In:                             http://www.linkedin.com/in/rpjday
Twitter:                                       http://twitter.com/rpjday
========================================================================


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