Messages in this thread | | | Date | Fri, 20 Jul 2012 17:35:39 -0600 | From | David Ahern <> | Subject | Re: perf with precise attribute kills all KVM based VMs |
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On 7/9/12 8:47 AM, Peter Zijlstra wrote: > On Mon, 2012-07-09 at 17:39 +0300, Avi Kivity wrote: >>> Disabling PEBS events for guests isn't pretty though.. >> >> We already have atomic MSR switching at guest entry/exit time. So it's >> not pretty in terms of not getting full profiling, but the code won't be >> too hard. Basically we just have to exclude_guest any pebs event. > > OK, so ideally we'd do something like the below, except of course that > that isn't backwards compatible and will break the world :/ > > bugger that > > --- > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -336,6 +338,9 @@ int x86_setup_perfctr(struct perf_event *event) > /* BTS is currently only allowed for user-mode. */ > if (!attr->exclude_kernel) > return -EOPNOTSUPP; > + > + if (!attr->exclude_guest) > + return -EOPNOTSUPP; > } > > hwc->config |= config; > @@ -378,6 +383,9 @@ int x86_pmu_hw_config(struct perf_event *event) > if (event->attr.precise_ip) { > int precise = 0; > > + if (!event->attr.exclude_guest) > + return -EOPNOTSUPP; > + > /* Support for constant skid */ > if (x86_pmu.pebs_active && !x86_pmu.pebs_broken) { > precise++; >
Tested-by: David Ahern <dsahern@gmail.com>
Gleb's patch is required as well. It takes both to fix the problem. And my userspace patch keeps compatibility for users who currently use -e cycles:pp (they won't be forced to add 'H'). (lkml is slow to show it so I can't pull a link for reference, but it's in your email ahead of this one).
Be nice to get this set into stable releases as well.
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