Re: [PATCH v2 5/5] KVM: MMU: lower the aduit frequency

Xiao Guangrong
2010-08-31T02:27:09Z

On 08/30/2010 11:47 PM, Marcelo Tosatti wrote:
> On Mon, Aug 30, 2010 at 06:26:33PM +0800, Xiao Guangrong wrote:
>> The audit is very high overhead, so we need lower the frequency to assure the guest running
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
>> ---
>> arch/x86/kvm/mmu_audit.c | 7 +++++++
>> 1 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/kvm/mmu_audit.c b/arch/x86/kvm/mmu_audit.c
>> index 3bde186..bd2b1be 100644
>> --- a/arch/x86/kvm/mmu_audit.c
>> +++ b/arch/x86/kvm/mmu_audit.c
>> @@ -17,6 +17,8 @@
>> *
>> */
>>
>> +#include <linux/ratelimit.h>
>> +
>> static const char *audit_msg;
>>
>> typedef void (*inspect_spte_fn) (struct kvm_vcpu *vcpu, u64 *sptep, int level);
>> @@ -228,6 +230,11 @@ static void audit_vcpu_spte(struct kvm_vcpu *vcpu)
>>
>> static void kvm_mmu_audit(void *ignore, struct kvm_vcpu *vcpu, int audit_point)
>> {
>> + static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
>> +
>> + if (!__ratelimit(&ratelimit_state))
>> + return;
>> +
>> audit_msg = audit_point_name[audit_point];
>> audit_all_active_sps(vcpu->kvm);
>> audit_vcpu_spte(vcpu);
>> --
>> 1.7.0.4
>
> Well, as Avi said this makes it difficult to trace back to offender (the
> audit points are placed around modifications to the shadow page tree
> for that reason).
>

Yeah. it's the best way that not rate limit it, but...

> I've always seen progress from the guest while running with audit
> enabled (its slow, but its not supposed to be fast anyway).
>
> Did you experience a freeze?
>

There is a simply test in the guest if it's not rate limit:

# time ls
anaconda-ks.cfg Documents install.log Music Public Videos
Desktop Downloads install.log.syslog Pictures Templates

real 1m26.053s
user 0m0.311s
sys 0m1.813s

'ls' command cost about 1.5 minute, if we run the memory test program, i think
the time/delay is unacceptable...... :-(