Messages in this thread | | | Date | Wed, 11 Jul 2012 22:11:57 -0600 | From | David Ahern <> | Subject | Re: perf with precise attribute kills all KVM based VMs |
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On 7/11/12 3:53 AM, Gleb Natapov wrote: > On Wed, Jul 11, 2012 at 11:49:47AM +0200, Peter Zijlstra wrote: >> On Wed, 2012-07-11 at 10:10 +0300, Gleb Natapov wrote: >> >>> Looks like Avi is right about the overshoot. Can you test something like this? >>> >>> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c >>> index 166546e..5fb371a 100644 >>> --- a/arch/x86/kernel/cpu/perf_event_intel.c >>> +++ b/arch/x86/kernel/cpu/perf_event_intel.c >>> @@ -1374,8 +1374,11 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr) >>> arr[0].msr = MSR_CORE_PERF_GLOBAL_CTRL; >>> arr[0].host = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask; >>> arr[0].guest = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_host_mask; >>> + arr[1].msr = MSR_IA32_PEBS_ENABLE; >>> + arr[1].host = cpuc->pebs_enabled; >>> + arr[1].guest = 0; >>> + *nr = 2; >>> >>> - *nr = 1; >>> return arr; >>> } >>
So far the 64-bit Fedora 10 VM with both a Fedora 10 stock kernel and a 2.6.38 kernel have not faired well - and that's the only VM I have tried at the moment. Using -e cycles:pp I have been able to lock up the VM 3 times out of 3 series of tests with perf-kvm that includes network traffic (e.g., netperf), disk I/O (dd based to create a file with dsync flag) and pure userspace cpu bound (openssl speed). May or may not be related.
Also, I noted that 'perf kvm --guest record -e cycles:pp' does not generate a whole lot of samples -- like < 100 in a 20-second sample -- despite the fact that the guest is rather busy.
I won't have much time over the next few days to run much in the way of tests; I'll come back to it Sunday night.
David
>> >> You also need to clear TR, BTS, BTINT from MSR_IA32_DEBUGCTLMSR and >> ideally you'd also clear MSR_IA32_DS_AREA so that any write will be a >> proper NULL deref or such. > Yes. With the patch above :pp modifier does not crash guest for me, but > in theory it should since BTS are still written to DS. May be BTS writes do > not overshoot guest entry. Will have to ask Intel for clarification.
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