Hi Pawel,
On Tue, 23 Sep 2014 18:03:06 +0100, Pawel Moll wrote:
> This patch adds an option to sample raw monotonic clock
> value with any perf event, with the the aim of allowing
> time correlation between data coming from perf and
> additional performance-related information generated in
> userspace.
>
> In order to correlate timestamps in perf data stream
> with events happening in userspace (be it JITed debug
> symbols or hwmon-originating environment data), user
> requests a more or less periodic event (sched_switch
> trace event of a hrtimer-based cpu-clock being the
> most obvious examples) with PERF_SAMPLE_TIME *and*
> PERF_SAMPLE_CLOCK_RAW_MONOTONIC and stamps
> user-originating data with values obtained from
> clock_gettime(CLOCK_MONOTONIC_RAW). Then, during
> analysis, one looks at the perf events immediately
> preceding and following (in terms of the
> clock_raw_monotonic sample) the userspace event and
> does simple linear approximation to get the equivalent
> perf time.
>
> perf event user event
> -----O--------------+-------------O------> t_mono
> : | :
> : V :
> -----O----------------------------O------> t_perf
Probably a dumb question: why not make PERF_SAMPLE_TIME being monotonic
clock instead of adding a new PERF_SAMPLE_CLOCK_XXX flag? Maybe we can
add a new ioctl command like PERF_EVENT_IOC_SET_CLOCK so that one can
pass a clock id.
Thanks,
Namhyung
>
> Signed-off-by: Pawel Moll <pawel.moll@xxxxxxx>
> ---
> Changes since v1:
>
> - none
>
> include/linux/perf_event.h | 2 ++
> include/uapi/linux/perf_event.h | 4 +++-
> kernel/events/core.c | 13 +++++++++++++
> 3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 707617a..28b73b2 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -602,6 +602,8 @@ struct perf_sample_data {
> * Transaction flags for abort events:
> */
> u64 txn;
> + /* Raw monotonic timestamp, for userspace time correlation */
> + u64 clock_raw_monotonic;
> };
>
> static inline void perf_sample_data_init(struct perf_sample_data *data,
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 9269de2..e5a75c5 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -137,8 +137,9 @@ enum perf_event_sample_format {
> PERF_SAMPLE_DATA_SRC = 1U << 15,
> PERF_SAMPLE_IDENTIFIER = 1U << 16,
> PERF_SAMPLE_TRANSACTION = 1U << 17,
> + PERF_SAMPLE_CLOCK_RAW_MONOTONIC = 1U << 18,
>
> - PERF_SAMPLE_MAX = 1U << 18, /* non-ABI */
> + PERF_SAMPLE_MAX = 1U << 19, /* non-ABI */
> };
>
> /*
> @@ -686,6 +687,7 @@ enum perf_event_type {
> * { u64 weight; } && PERF_SAMPLE_WEIGHT
> * { u64 data_src; } && PERF_SAMPLE_DATA_SRC
> * { u64 transaction; } && PERF_SAMPLE_TRANSACTION
> + * { u64 clock_raw_monotonic; } && PERF_SAMPLE_CLOCK_RAW_MONOTONIC
> * };
> */
> PERF_RECORD_SAMPLE = 9,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index f9c1ed0..f6df547 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1216,6 +1216,9 @@ static void perf_event__header_size(struct perf_event *event)
> if (sample_type & PERF_SAMPLE_TRANSACTION)
> size += sizeof(data->txn);
>
> + if (sample_type & PERF_SAMPLE_CLOCK_RAW_MONOTONIC)
> + size += sizeof(data->clock_raw_monotonic);
> +
> event->header_size = size;
> }
>
> @@ -4456,6 +4459,13 @@ static void __perf_event_header__init_id(struct perf_event_header *header,
> data->cpu_entry.cpu = raw_smp_processor_id();
> data->cpu_entry.reserved = 0;
> }
> +
> + if (sample_type & PERF_SAMPLE_CLOCK_RAW_MONOTONIC) {
> + struct timespec now;
> +
> + getrawmonotonic(&now);
> + data->clock_raw_monotonic = timespec_to_ns(&now);
> + }
> }
>
> void perf_event_header__init_id(struct perf_event_header *header,
> @@ -4714,6 +4724,9 @@ void perf_output_sample(struct perf_output_handle *handle,
> if (sample_type & PERF_SAMPLE_TRANSACTION)
> perf_output_put(handle, data->txn);
>
> + if (sample_type & PERF_SAMPLE_CLOCK_RAW_MONOTONIC)
> + perf_output_put(handle, data->clock_raw_monotonic);
> +
> if (!event->attr.watermark) {
> int wakeup_events = event->attr.wakeup_events;
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