On 09/24/2012 09:36 PM, Avi Kivity wrote:
On 09/24/2012 05:41 PM, Avi Kivity wrote:
case 2)
rq1 : vcpu1->wait(lockA) (spinning)
rq2 : vcpu3 (running) , vcpu2->holding(lockA) [scheduled out]
I agree that checking rq1 length is not proper in this case, and as you
rightly pointed out, we are in trouble here.
nr_running()/num_online_cpus() would give more accurate picture here,
but it seemed costly. May be load balancer save us a bit here in not
running to such sort of cases. ( I agree load balancer is far too
complex).
In theory preempt notifier can tell us whether a vcpu is preempted or
not (except for exits to userspace), so we can keep track of whether
it's we're overcommitted in kvm itself. It also avoids false positives
from other guests and/or processes being overcommitted while our vm is fine.
It also allows us to cheaply skip running vcpus.
Hi Avi,
Could you please elaborate on how preempt notifiers can be used
here to keep track of overcommit or skip running vcpus?
Are we planning set some flag in sched_out() handler etc?
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