From: Andrew Morton <akpm@linux-foundation.org>
To: Avi Kivity <avi@qumranet.com>
Cc: kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@elte.hu>
Subject: kvm warning
Date: Wed, 8 Aug 2007 15:14:46 -0700 [thread overview]
Message-ID: <20070808151446.9a4eebda.akpm@linux-foundation.org> (raw)
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 <avi@qumranet.com>
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 <shaohua.li@intel.com>.
Signed-off-by: Avi Kivity <avi@qumranet.com>
--- 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...
next reply other threads:[~2007-08-08 22:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-08 22:14 Andrew Morton [this message]
2007-08-08 22:19 ` kvm warning Ingo Molnar
2007-08-08 22:48 ` Avi Kivity
2007-08-08 22:59 ` Andrew Morton
2007-08-08 23:09 ` Avi Kivity
2007-08-13 17:31 ` Satyam Sharma
2007-08-13 17:37 ` Luck, Tony
2007-08-13 18:11 ` Satyam Sharma
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