Re: perf_counter Atom patch

From: stephane eranian
Date: Tue Jun 23 2009 - 04:40:57 EST


On Tue, Jun 23, 2009 at 10:27 AM, stephane
eranian<eranian@xxxxxxxxxxxxxx> wrote:
> Hi,
> On Tue, Jun 23, 2009 at 9:59 AM, Yong Wang<> wrote:
>> On Tue, Jun 23, 2009 at 09:45:03AM +0200, stephane eranian wrote:
>>> Unfortunately, I don't have a N270 to compare with your results.
>>> We need to verify whether or not N270 implements the fixed counters.
>>> Does it report architected perfmon v3 or v1?
>> All Atom processors report perfmon v3 as specified in SDM. N270 is no
>> exception.
> V3 does not set a minimal number of fixed counters, could be zero. But
> that seems
> odd. Let me ask around.
Second thought on this:
x86_pmu.num_counters_fixed =
max((int)edx.split.num_counters_fixed, 3);

rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, x86_pmu.intel_ctrl);

Forcing num_counter_fixed is not enough, you need to make sure they are actually
activated in GLOBAL_CTRL, i.e., make sure bits 32-34 are set in intel_ctrl.
Depending on which machine you're on, the power on value for GLOBAL_CTRL
changes. The correct value for it should be that ONLY generic counters are on
by default.
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