Re: perf with precise attribute kills all KVM based VMs
From: David Ahern
Date: Thu Jul 12 2012 - 00:12:47 EST
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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