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    SubjectRe: [[PATCH v6 02/10] perf: Add a flags parameter to pmu txn interfaces
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    On Thu, 2015-09-03 at 20:07 -0700, Sukadev Bhattiprolu wrote:
    > Currently, the PMU interface allows reading only one counter at a time.
    > But some PMUs like the 24x7 counters in Power, support reading several
    > counters at once. To leveage this functionality, extend the transaction
    > interface to support a "transaction type".
    >
    > The first type, PERF_PMU_TXN_ADD, refers to the existing transactions,
    > i.e. used to _schedule_ all the events on the PMU as a group. A second
    > transaction type, PERF_PMU_TXN_READ, will be used in a follow-on patch,
    > by the 24x7 counters to read several counters at once.
    >
    > Extend the transaction interfaces to the PMU to accept a 'txn_flags'
    > parameter and use this parameter to ignore any transactions that are
    > not of type PERF_PMU_TXN_ADD.
    >
    > Thanks to Peter Zijlstra for his input.
    >
    > Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
    >
    > ---
    > arch/powerpc/perf/core-book3s.c | 30 +++++++++++++++++++++++++++++-

    These powerpc changes look OK to me.

    So for those you can have an:

    Acked-by: Michael Ellerman <mpe@ellerman.id.au>


    Having said that, we do end up repeating a lot of boiler plate for each arch,
    which is a pity. eg:

    > +static void power_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags)
    > {
    > struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
    >
    > + WARN_ON_ONCE(cpuhw->txn_flags); /* txn already in flight */
    > +
    > + cpuhw->txn_flags = txn_flags;
    > + if (txn_flags & ~PERF_PMU_TXN_ADD)
    > + return;
    > +

    And so on.

    But I can't think of an easy way to avoid that, so it's not a blocker, but
    maybe someone can think of a nice solution to avoid it?

    cheers





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