Re: perf with precise attribute kills all KVM based VMs
From: David Ahern
Date: Thu Jul 12 2012 - 11:20:53 EST
On 7/11/12 10:29 PM, Gleb Natapov wrote:
On Wed, Jul 11, 2012 at 10:11:57PM -0600, David Ahern wrote:
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.
OK that's may be BTSes. What about -e cycles:p? BTW are you using your
patch to set exclude_guest parameter? If not use -e cycles:Hp.
I started with cycles:pp; should not really matter - they all need to
work without blowing up VMs (cycles:p, cycles:pH, cycles:pG, cycles:pp,
cycles:ppH, cycles:ppG).
For grins I ran a quick test while reading emails this morning. This
time a fedora 17 VM with 3.4.0-1.fc17.x86_64 kernel. It too locks up
pretty quickly - just a couple of iterations of perf:
perf kvm --guestmount=/tmp/guest-mount record -fo /tmp/perf.data -a -v
-e cycles:pH -- sleep 60
Note the :pH this time.
I did not have netserver installed in the VM so used a ping flood for
network traffic.
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.
Host events do not suppose to generate events while guest is running.
My server has 16 cpus and the VM has only 2 vcpus; with the -a I would
expect some host sampling. Note: in the above case :pp resets the
exclude-host modifier set by the perf-kvm part, so hosts samples are not
excluded. See parse_events_modifier().
So, is the idea of your patch to not enable the PEBS in guest mode?
David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/