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    SubjectRe: [PATCH V4 09/10] power8, perf: Change BHRB branch filter configuration
    Date
    On Wed, 2013-04-12 at 10:32:41 UTC, Anshuman Khandual wrote:
    > Powerpc kernel now supports SW based branch filters for book3s systems with some
    > specifc requirements while dealing with HW supported branch filters in order to
    > achieve overall OR semantics prevailing in perf branch stack sampling framework.
    > This patch adapts the BHRB branch filter configuration to meet those protocols.
    > POWER8 PMU does support 3 branch filters (out of which two are getting used in
    > perf branch stack) which are mutually exclussive and cannot be ORed with each
    > other. This implies that PMU can only handle one HW based branch filter request
    > at any point of time. For all other combinations PMU will pass it on to the SW.
    >
    > Also the combination of PERF_SAMPLE_BRANCH_ANY_CALL and PERF_SAMPLE_BRANCH_COND
    > can now be handled in SW, hence we dont error them out anymore.
    >
    > diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
    > index 03c5b8d..6021349 100644
    > --- a/arch/powerpc/perf/power8-pmu.c
    > +++ b/arch/powerpc/perf/power8-pmu.c
    > @@ -561,7 +561,56 @@ static int power8_generic_events[] = {
    >
    > static u64 power8_bhrb_filter_map(u64 branch_sample_type, u64 *filter_mask)
    > {
    > - u64 pmu_bhrb_filter = 0;
    > + u64 x, tmp, pmu_bhrb_filter = 0;
    > + *filter_mask = 0;
    > +
    > + /* No branch filter requested */
    > + if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY) {
    > + *filter_mask = PERF_SAMPLE_BRANCH_ANY;
    > + return pmu_bhrb_filter;
    > + }
    > +
    > + /*
    > + * P8 does not support oring of PMU HW branch filters. Hence
    > + * if multiple branch filters are requested which includes filters
    > + * supported in PMU, still go ahead and clear the PMU based HW branch
    > + * filter component as in this case all the filters will be processed
    > + * in SW.

    Leading space there.

    > + */
    > + tmp = branch_sample_type;
    > +
    > + /* Remove privilege filters before comparison */
    > + tmp &= ~PERF_SAMPLE_BRANCH_USER;
    > + tmp &= ~PERF_SAMPLE_BRANCH_KERNEL;
    > + tmp &= ~PERF_SAMPLE_BRANCH_HV;
    > +
    > + for_each_branch_sample_type(x) {
    > + /* Ignore privilege requests */
    > + if ((x == PERF_SAMPLE_BRANCH_USER) || (x == PERF_SAMPLE_BRANCH_KERNEL) || (x == PERF_SAMPLE_BRANCH_HV))
    > + continue;
    > +
    > + if (!(tmp & x))
    > + continue;
    > +
    > + /* Supported HW PMU filters */
    > + if (tmp & PERF_SAMPLE_BRANCH_ANY_CALL) {
    > + tmp &= ~PERF_SAMPLE_BRANCH_ANY_CALL;
    > + if (tmp) {
    > + pmu_bhrb_filter = 0;
    > + *filter_mask = 0;
    > + return pmu_bhrb_filter;
    > + }
    > + }
    > +
    > + if (tmp & PERF_SAMPLE_BRANCH_COND) {
    > + tmp &= ~PERF_SAMPLE_BRANCH_COND;
    > + if (tmp) {
    > + pmu_bhrb_filter = 0;
    > + *filter_mask = 0;
    > + return pmu_bhrb_filter;
    > + }
    > + }
    > + }

    >
    > /* BHRB and regular PMU events share the same privilege state
    > * filter configuration. BHRB is always recorded along with a
    > @@ -570,34 +619,20 @@ static u64 power8_bhrb_filter_map(u64 branch_sample_type, u64 *filter_mask)
    > * PMU event, we ignore any separate BHRB specific request.
    > */
    >
    > - /* No branch filter requested */
    > - if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY)
    > - return pmu_bhrb_filter;
    > -
    > - /* Invalid branch filter options - HW does not support */
    > - if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY_RETURN)
    > - return -1;
    > -
    > - if (branch_sample_type & PERF_SAMPLE_BRANCH_IND_CALL)
    > - return -1;
    > -
    > + /* Supported individual branch filters */
    > if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY_CALL) {
    > pmu_bhrb_filter |= POWER8_MMCRA_IFM1;
    > + *filter_mask |= PERF_SAMPLE_BRANCH_ANY_CALL;
    > return pmu_bhrb_filter;
    > }
    >
    > if (branch_sample_type & PERF_SAMPLE_BRANCH_COND) {
    > pmu_bhrb_filter |= POWER8_MMCRA_IFM3;
    > + *filter_mask |= PERF_SAMPLE_BRANCH_COND;
    > return pmu_bhrb_filter;
    > }
    >
    > - /* PMU does not support ANY combination of HW BHRB filters */
    > - if ((branch_sample_type & PERF_SAMPLE_BRANCH_ANY_CALL) &&
    > - (branch_sample_type & PERF_SAMPLE_BRANCH_COND))
    > - return -1;
    > -
    > - /* Every thing else is unsupported */
    > - return -1;
    > + return pmu_bhrb_filter;
    > }


    As I said in my comments on version 3 which you ignored:

    I think it would be clearer if we actually checked for the possibilities we
    allow and let everything else fall through, eg:

            /* Ignore user/kernel/hv bits */
            branch_sample_type &= ~PERF_SAMPLE_BRANCH_PLM_ALL;

            if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY)
                    return 0;

            if (branch_sample_type == PERF_SAMPLE_BRANCH_ANY_CALL)
                    return POWER8_MMCRA_IFM1;
     
            if (branch_sample_type == PERF_SAMPLE_BRANCH_COND)
                    return POWER8_MMCRA_IFM3;
            
            return -1;


    cheers
    --
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