linux-kernel - Re: [PATCH 4/4] KVM: MMU: lower the aduit frequency

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Date:	Mon, 30 Aug 2010 10:16:38 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 4/4] KVM: MMU: lower the aduit frequency

On 08/29/2010 05:19 PM, Avi Kivity wrote:
>  On 08/28/2010 03:03 PM, Xiao Guangrong wrote:
>> The audit is very high overhead, so we need lower the frequency to
>> assure the guest running
>>
>>
>>    */
>>
>>   #include<linux/debugfs.h>
>> +#include<linux/ratelimit.h>
>>
>>   static struct dentry *debugfs_file;
>>   static bool mmu_debug;
>> @@ -233,6 +234,11 @@ static void audit_vcpu_spte(struct kvm_vcpu *vcpu)
>>
>>   static void kvm_mmu_audit(void *ignore, struct kvm_vcpu *vcpu, const
>> char *msg)
>>   {
>> +    static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
>> +
>> +    if (!__ratelimit(&ratelimit_state))
>> +        return;
>> +
>>       audit_msg = msg;
>>       audit_all_active_sps(vcpu->kvm);
>>       audit_vcpu_spte(vcpu);
> 
> This means we see a bug long after it happened, so we can't correlate it
> to the cause.
> 
> It's fine as an option (even the default) but I'd like to be able to
> audit after every operation.  Perhaps a partial audit that only looks at
> the gfns and vaddrs that were affected in the last operation?
> 

Audit checks all the active shadow pages and all vcpu's page table, so the
overload is very high :-)

During my test, if enable the aduit, the guest mostly hung, it means the guest
not do anything.
(Host: Intel(R) Xeon(R) X3430  @ 2.40GHz * 4 + 4G memory
 GUest: x2VCPU + 1G memory
)

I'll set the 'ratelimit' as a module parameter, then if the user's machine is
fast enough, the ratelimit can be disabled.
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