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    SubjectRe: [PATCH v7 07/12] perf/x86: no counter allocation support
    On Mon, Jul 08, 2019 at 09:23:14AM +0800, Wei Wang wrote:
    > In some cases, an event may be created without needing a counter
    > allocation. For example, an lbr event may be created by the host
    > only to help save/restore the lbr stack on the vCPU context switching.
    >
    > This patch adds a new interface to allow users to create a perf event
    > without the need of counter assignment.
    >
    > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
    > Cc: Andi Kleen <ak@linux.intel.com>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > ---

    I _really_ hate this one.

    > arch/x86/events/core.c | 12 ++++++++++++
    > include/linux/perf_event.h | 13 +++++++++++++
    > kernel/events/core.c | 37 +++++++++++++++++++++++++------------
    > 3 files changed, 50 insertions(+), 12 deletions(-)
    >
    > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
    > index f315425..eebbd65 100644
    > --- a/arch/x86/events/core.c
    > +++ b/arch/x86/events/core.c
    > @@ -410,6 +410,9 @@ int x86_setup_perfctr(struct perf_event *event)
    > struct hw_perf_event *hwc = &event->hw;
    > u64 config;
    >
    > + if (is_no_counter_event(event))
    > + return 0;
    > +
    > if (!is_sampling_event(event)) {
    > hwc->sample_period = x86_pmu.max_period;
    > hwc->last_period = hwc->sample_period;
    > @@ -1248,6 +1251,12 @@ static int x86_pmu_add(struct perf_event *event, int flags)
    > hwc = &event->hw;
    >
    > n0 = cpuc->n_events;
    > +
    > + if (is_no_counter_event(event)) {
    > + n = n0;
    > + goto done_collect;
    > + }
    > +
    > ret = n = collect_events(cpuc, event, false);
    > if (ret < 0)
    > goto out;
    > @@ -1422,6 +1431,9 @@ static void x86_pmu_del(struct perf_event *event, int flags)
    > if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
    > goto do_del;
    >
    > + if (is_no_counter_event(event))
    > + goto do_del;
    > +
    > /*
    > * Not a TXN, therefore cleanup properly.
    > */

    That's truely an abomination.

    > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    > index 0ab99c7..19e6593 100644
    > --- a/include/linux/perf_event.h
    > +++ b/include/linux/perf_event.h
    > @@ -528,6 +528,7 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
    > */
    > #define PERF_EV_CAP_SOFTWARE BIT(0)
    > #define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
    > +#define PERF_EV_CAP_NO_COUNTER BIT(2)
    >
    > #define SWEVENT_HLIST_BITS 8
    > #define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
    > @@ -895,6 +896,13 @@ extern int perf_event_refresh(struct perf_event *event, int refresh);
    > extern void perf_event_update_userpage(struct perf_event *event);
    > extern int perf_event_release_kernel(struct perf_event *event);
    > extern struct perf_event *
    > +perf_event_create(struct perf_event_attr *attr,
    > + int cpu,
    > + struct task_struct *task,
    > + perf_overflow_handler_t overflow_handler,
    > + void *context,
    > + bool counter_assignment);
    > +extern struct perf_event *
    > perf_event_create_kernel_counter(struct perf_event_attr *attr,
    > int cpu,
    > struct task_struct *task,

    Why the heck are you creating this wrapper nonsense?

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