Messages in this thread | | | Date | Mon, 30 Aug 2010 09:59:06 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 4/4] KVM: MMU: lower the aduit frequency |
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On 08/30/2010 05:16 AM, Xiao Guangrong wrote: > 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 > )
You're right, I remember that from the last time I used audit many years ago.
> I'll set the 'ratelimit' as a module parameter, then if the user's machine is > fast enough, the ratelimit can be disabled.
It's only useful in very special cases - low memory and a very fast reproducer. I think we can live without the parameter, if someone has this special case they can hack the code.
-- error compiling committee.c: too many arguments to function
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