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    SubjectRe: [PATCH v4 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter
    On 07/28/2015 01:17 PM, Kaixu Xia wrote:
    > According to the perf_event_map_fd and index, the function
    > bpf_perf_event_read() can convert the corresponding map
    > value to the pointer to struct perf_event and return the
    > Hardware PMU counter value.
    >
    > Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
    > ---
    > include/linux/bpf.h | 1 +
    > include/linux/perf_event.h | 3 ++-
    > include/uapi/linux/bpf.h | 1 +
    > kernel/bpf/helpers.c | 36 ++++++++++++++++++++++++++++++++++++
    > kernel/events/core.c | 4 ++--
    > kernel/trace/bpf_trace.c | 2 ++
    > 6 files changed, 44 insertions(+), 3 deletions(-)
    >
    > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
    > index 3c9c0eb..516992c 100644
    > --- a/include/linux/bpf.h
    > +++ b/include/linux/bpf.h
    > @@ -190,6 +190,7 @@ extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
    > extern const struct bpf_func_proto bpf_map_update_elem_proto;
    > extern const struct bpf_func_proto bpf_map_delete_elem_proto;
    >
    > +extern const struct bpf_func_proto bpf_perf_event_read_proto;
    > extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
    > extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
    > extern const struct bpf_func_proto bpf_tail_call_proto;
    > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    > index 2ea4067..899abcb 100644
    > --- a/include/linux/perf_event.h
    > +++ b/include/linux/perf_event.h
    > @@ -662,7 +662,8 @@ extern void perf_pmu_migrate_context(struct pmu *pmu,
    > int src_cpu, int dst_cpu);
    > extern u64 perf_event_read_value(struct perf_event *event,
    > u64 *enabled, u64 *running);
    > -
    > +extern void __perf_event_read(void *info);
    > +extern u64 perf_event_count(struct perf_event *event);
    >
    > struct perf_sample_data {
    > /*
    > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
    > index 69a1f6b..b9b13ce 100644
    > --- a/include/uapi/linux/bpf.h
    > +++ b/include/uapi/linux/bpf.h
    > @@ -250,6 +250,7 @@ enum bpf_func_id {
    > * Return: 0 on success
    > */
    > BPF_FUNC_get_current_comm,
    > + BPF_FUNC_perf_event_read, /* u64 bpf_perf_event_read(&map, index) */
    > __BPF_FUNC_MAX_ID,
    > };
    >
    > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
    > index 1447ec0..c40c5ea 100644
    > --- a/kernel/bpf/helpers.c
    > +++ b/kernel/bpf/helpers.c
    > @@ -182,3 +182,39 @@ const struct bpf_func_proto bpf_get_current_comm_proto = {
    > .arg1_type = ARG_PTR_TO_STACK,
    > .arg2_type = ARG_CONST_STACK_SIZE,
    > };
    > +
    > +static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
    > +{
    > + struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
    > + struct bpf_array *array = container_of(map, struct bpf_array, map);
    > + struct perf_event *event;
    > +
    > + if (index >= array->map.max_entries)
    > + return -E2BIG;

    Maybe unlikely(...), likewise below.

    > + event = (struct perf_event *)array->ptrs[index];
    > + if (!event)
    > + return -ENOENT;
    > +
    > + if (event->state != PERF_EVENT_STATE_ACTIVE)
    > + return -EINVAL;
    > +
    > + if (event->oncpu != raw_smp_processor_id() &&
    > + event->ctx->task != current)
    > + return -EINVAL;
    > +
    > + if (event->attr.inherit)
    > + return -EINVAL;
    > +
    > + __perf_event_read(event);
    > +
    > + return perf_event_count(event);

    I believe this helper should rather go somewhere such as bpf_trace.c
    (or under kernel/events/ ?), wouldn't we otherwise get a build error
    when perf events are compiled out?

    Anyway, I let perf folks comment on that (and the helper in general).

    > +}
    > +
    > +const struct bpf_func_proto bpf_perf_event_read_proto = {
    > + .func = bpf_perf_event_read,
    > + .gpl_only = false,
    > + .ret_type = RET_INTEGER,
    > + .arg1_type = ARG_CONST_MAP_PTR,
    > + .arg2_type = ARG_ANYTHING,
    > +};
    > diff --git a/kernel/events/core.c b/kernel/events/core.c
    > index 58f0d47..c926c6d 100644
    > --- a/kernel/events/core.c
    > +++ b/kernel/events/core.c
    > @@ -3177,7 +3177,7 @@ void perf_event_exec(void)
    > /*
    > * Cross CPU call to read the hardware event
    > */
    > -static void __perf_event_read(void *info)
    > +void __perf_event_read(void *info)

    Does this need to be declared in a header file, no?

    > {
    > struct perf_event *event = info;
    > struct perf_event_context *ctx = event->ctx;
    > @@ -3204,7 +3204,7 @@ static void __perf_event_read(void *info)
    > raw_spin_unlock(&ctx->lock);
    > }
    >
    > -static inline u64 perf_event_count(struct perf_event *event)
    > +u64 perf_event_count(struct perf_event *event)

    Likewise? Should the inlining be preserved?

    > {
    > if (event->pmu->count)
    > return event->pmu->count(event);
    > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
    > index 88a041a..9cf094f 100644
    > --- a/kernel/trace/bpf_trace.c
    > +++ b/kernel/trace/bpf_trace.c
    > @@ -183,6 +183,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func

    Btw, I'm wondering if the perf event map portions should actually better go
    here into bpf_trace.c ...

    > return bpf_get_trace_printk_proto();
    > case BPF_FUNC_get_smp_processor_id:
    > return &bpf_get_smp_processor_id_proto;
    > + case BPF_FUNC_perf_event_read:
    > + return &bpf_perf_event_read_proto;
    > default:
    > return NULL;
    > }
    >



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