ia64 allmodconfig says
drivers/kvm/Kconfig:14:warning: 'select' used by config symbol 'KVM' refers to undefined symbol 'PREEMPT_NOTIFIERS'
Because of
commit 8928fb48c7a7f9053a55f1d0023cbc533f2b3663
Author: Avi Kivity <[email protected]>
Date: Wed Jul 11 18:17:21 2007 +0300
KVM: Use the scheduler preemption notifiers to make kvm preemptible
Current kvm disables preemption while the new virtualization registers are
in use. This of course is not very good for latency sensitive workloads (on
use of virtualization is to offload user interface and other latency
insensitive stuff to a container, so that it is easier to analyze the
remaining workload). This patch re-enables preemption for kvm; preemption
is now only disabled when switching the registers in and out, and during
the switch to guest mode and back.
Contains fixes from Shaohua Li <[email protected]>.
Signed-off-by: Avi Kivity <[email protected]>
--- a/drivers/kvm/Kconfig
+++ b/drivers/kvm/Kconfig
@@ -11,6 +11,7 @@ if VIRTUALIZATION
config KVM
tristate "Kernel-based Virtual Machine (KVM) support"
depends on X86 && EXPERIMENTAL
+ select PREEMPT_NOTIFIERS
select ANON_INODES
---help---
Support hosting fully virtualized guest machines using hardware
...
a) is kvm supported on ia64 at all??
b) `select' is evil. Just Don't Do It.
c) `select' is especially evil when it's done on some kernel-internal
secret symbol like PREEMPT_NOTIFIERS.
d) I can't see anything else in the kernel which sets or clears
PREEMPT_NOTIFIERS so I'm rather wonderring why the config option exists
at all.
e) sched developers may not like KVM reaching over and twiddling their
knobs for them.
It all needs more thought, I think...
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