linux-kernel - Re: [kvm-devel] [PATCH 2/2] KVM: Use the scheduler preemption hooks to make kvm preemptible

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Date:	Thu, 12 Jul 2007 08:43:08 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Luca <kronos.it@...il.com>
CC:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 2/2] KVM: Use the scheduler preemption hooks
 to make kvm preemptible

Luca wrote:
> On 7/11/07, Avi Kivity <avi@...ranet.com> wrote:
>> Current kvm disables preemption while the new virtualization
>> registers are
>> in use.  This of course is not very good for latency sensitive
>> workloads (one
>> 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.
> [...]
>> diff --git a/drivers/kvm/Kconfig b/drivers/kvm/Kconfig
>> index 33fa28a..92644b5 100644
>> --- a/drivers/kvm/Kconfig
>> +++ b/drivers/kvm/Kconfig
>> @@ -10,7 +10,7 @@ if VIRTUALIZATION
>>
>>  config KVM
>>         tristate "Kernel-based Virtual Machine (KVM) support"
>> -       depends on X86 && EXPERIMENTAL
>> +       depends on X86 && EXPERIMENTAL && PREEMPT_HOOKS
>>         depends on X86_CMPXCHG64 || 64BIT
>
> select PREEMPT_HOOKS maybe?
>

Yes.  And default PREEMPT_HOOKS to n in the first patch.  I'll make both
these changes.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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