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

Xiao Guangrong
2010-08-30T02:12:23Z

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.