Re: [PATCH RFC 0/2] assign each vcpu an owning thread and improve yielding

[David Hildenbrand <dahi@linux.vnet.ibm.com>]

> 
> 
> On 03/12/2014 13:12, David Hildenbrand wrote:
> >> This series improves yielding on architectures that cannot disable preemption
> >> while entering the guest and makes the creating thread of a VCPU the owning
> >> thread and therefore the yield target when yielding to that VCPU.
> >>
> >> We should focus on the case creating thread == executing thread and therefore
> >> remove the complicated handling of PIDs involving synchronize_rcus.
> >>
> >> This way we can speed up the creation of VCPUs and directly yield to the
> >> executing vcpu threads.
> >>
> >> Please note that - in theory - all VCPU ioctls should be triggered from the same
> >> VCPU thread, so changing threads is not a scenario we should optimize.
> >>
> >>
> >> David Hildenbrand (2):
> >>   KVM: don't check for PF_VCPU when yielding
> >>   KVM: thread creating a vcpu is the owner of that vcpu
> >>
> >>  include/linux/kvm_host.h |  1 +
> >>  virt/kvm/kvm_main.c      | 22 ++--------------------
> >>  2 files changed, 3 insertions(+), 20 deletions(-)
> >>
> > 
> > Hi Paolo,
> > 
> > would be good if you could have a look at these patches.
> 
> Sure.
> 
> I think patch 1 is fine and I am applying it.  For patch 2, what about
> moving the ->pid assignment in the KVM_RUN case of kvm_vcpu_ioctl?

Thanks Paolo!

Well, do we have any known user that relies on this thread-switching in case
of KVM_RUN? If yes, I am totally with you.

If not I'd prefer to get this code completely out, as it contains some
unnecessary complexity. And maintaining such code that already had a couple of
bugs in it without any benefit doesn't make much sense. What do you think?

David

> 
> Paolo
>