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    SubjectRe: [PATCH 0/4] perf: Intel uncore pmu counting support
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    On Fri, Jul 1, 2011 at 2:23 PM, Stephane Eranian <eranian@google.com> wrote:
    > Lin,
    >
    > Ok, false alarm. Vol3b is correct. I missed the fact that if you want
    > wrmsrl() to write full width generic counters, you have to use the
    > alternate MSR alias. I guess that's for backward compatibility.
    > So for full width wrmsrl on PERFCTR0 -> use 0x41c
    >
    > uncore counter value: 0x678ffffeeee
    > core fixed counter value: 0x678ffffeeee
    >       core generic counter value: 0xffffffffeeee
    > wide core generic counter value: 0x678ffffeeee
    >
    > I think full width write to fixed counters has been there
    > for a long time. Looks like the problem was only present
    > for core generic counters until SNB.
    >
    Forgot to say, that we could adapt the code to use the alternate
    registers if full width wrmsrl() is supported. That would mitigate
    a bit the overhead of sampling and counting by simply not interrupting
    that often to accumulate counts in the SW counter.
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