Re: [RESEND PATCH 09/12] perf: Extend perf_output_read

Peter Zijlstra
2024-06-20T09:00:33Z

On Tue, Jun 18, 2024 at 08:10:41AM -0700, kan.liang@linux.intel.com wrote:
> From: Kan Liang <kan.liang@linux.intel.com>
>
> The event may have been updated in the PMU-specific implementation,
> e.g., Intel PEBS counters snapshotting. The common code should not
> read and overwrite the value.
>
> The PERF_SAMPLE_READ in the data->sample_type can be used to detect
> whether the PMU-specific value is available. If yes, avoid the
> pmu->read() in the common code.
>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> ---
> kernel/events/core.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 8f908f077935..733e507948e6 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7243,7 +7243,7 @@ static void perf_output_read_one(struct perf_output_handle *handle,
>
> static void perf_output_read_group(struct perf_output_handle *handle,
> struct perf_event *event,
> - u64 enabled, u64 running)
> + u64 enabled, u64 running, bool read)
> {
> struct perf_event *leader = event->group_leader, *sub;
> u64 read_format = event->attr.read_format;
> @@ -7265,7 +7265,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
> values[n++] = running;
>
> - if ((leader != event) &&
> + if ((leader != event) && read &&
> (leader->state == PERF_EVENT_STATE_ACTIVE))
> leader->pmu->read(leader);
>
> @@ -7280,7 +7280,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> for_each_sibling_event(sub, leader) {
> n = 0;
>
> - if ((sub != event) &&
> + if ((sub != event) && read &&
> (sub->state == PERF_EVENT_STATE_ACTIVE))
> sub->pmu->read(sub);
>
> @@ -7307,7 +7307,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
> * on another CPU, from interrupt/NMI context.
> */
> static void perf_output_read(struct perf_output_handle *handle,
> - struct perf_event *event)
> + struct perf_event *event,
> + bool read)
> {
> u64 enabled = 0, running = 0, now;
> u64 read_format = event->attr.read_format;
> @@ -7325,7 +7326,7 @@ static void perf_output_read(struct perf_output_handle *handle,
> calc_timer_values(event, &now, &enabled, &running);
>
> if (event->attr.read_format & PERF_FORMAT_GROUP)
> - perf_output_read_group(handle, event, enabled, running);
> + perf_output_read_group(handle, event, enabled, running, read);
> else
> perf_output_read_one(handle, event, enabled, running);
> }
> @@ -7367,7 +7368,7 @@ void perf_output_sample(struct perf_output_handle *handle,
> perf_output_put(handle, data->period);
>
> if (sample_type & PERF_SAMPLE_READ)
> - perf_output_read(handle, event);
> + perf_output_read(handle, event, !(data->sample_flags & PERF_SAMPLE_READ));
>
> if (sample_type & PERF_SAMPLE_CALLCHAIN) {
> int size = 1;

this can't be right. The output is order sensitive. If a
PERF_SAMPLE_READ is part of the PERF_RECORD_SAMPLE, it must be in this
location.