Messages in this thread Patch in this message | | | Date | Fri, 5 Jun 2015 17:42:47 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] perf: honoring the architectural performance monitoring version |
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On Fri, Jun 05, 2015 at 05:28:45PM +0200, Imre Palik wrote: > From: "Palik, Imre" <imrep@amazon.de> > > Architectural performance monitoring version 1 doesn't support fixed > counters. Currently, even if a hypervisor advertises support for > architectural performance monitoring version 1, perf may still tries to use > the fixed counters, as the constraints are set up based on the CPU model. > > This patch ensures that perf honors the architectural performance > monitoring version returned by CPUID, and it only uses the fixed counters > for version two and above. > > Some of the ideas in this patch are coming from Peter Zijlstra. > > Signed-off-by: Imre Palik <imrep@amazon.de> > Cc: Anthony Liguori <aliguori@amazon.com> > --- > arch/x86/kernel/cpu/perf_event_intel.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c > index 3998131..bde66aa 100644 > --- a/arch/x86/kernel/cpu/perf_event_intel.c > +++ b/arch/x86/kernel/cpu/perf_event_intel.c > @@ -1870,7 +1870,7 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, int idx, > for_each_event_constraint(c, x86_pmu.event_constraints) { > if ((event->hw.config & c->cmask) == c->code) { > event->hw.flags |= c->flags; > - return c; > + return c->idxmsk64 ? c : NULL;
One too many spaces there :-) Returning c as found, even with empty idxmsk is fine.
Also, I think this is broken, I think we hard assume x86_get_event_constraints() returns a valid constraint, see for example:
x86_schedule_event():
c = x86_pmu.get_event_constraints() = intel_get_event_constraints() = __intel_get_event_constraints() = x86_get_event_constraints();
cpuc->event_constraint[i] = c;
...
c = cpuc->event_constraint[i];
if (!test_bit(hwc->idx, c->idxmask)) <-- *boom*
> @@ -3341,9 +3341,12 @@ __init int intel_pmu_init(void) > for_each_event_constraint(c, x86_pmu.event_constraints) { > if (c->cmask != FIXED_EVENT_FLAGS > || c->idxmsk64 == INTEL_PMC_MSK_FIXED_REF_CYCLES) { > + c->idxmsk64 &= > + ~(~0UL << (INTEL_PMC_IDX_FIXED + x86_pmu.num_counters_fixed));
If you change idxmsk64 you also need to update weight.
> continue; > } > - > + c->idxmsk64 &= > + ~(~0UL << (INTEL_PMC_IDX_FIXED + x86_pmu.num_counters_fixed)); > c->idxmsk64 |= (1ULL << x86_pmu.num_counters) - 1; > c->weight += x86_pmu.num_counters;
And since we're now not unconditionally adding num_counters bits, that weight update is broken.
For both sites, something like:
c->weight = hweight64(c->idxmsk64);
Will recompute the weight.
Thanks!
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