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    SubjectRe: perf with precise attribute kills all KVM based VMs
    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


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