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SubjectRe: [PATCH V5 09/12] perf: make events stream always parsable
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On Tue, Jul 16, 2013 at 5:09 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Jul 16, 2013 at 09:49:31AM +0300, Adrian Hunter wrote:
>
>> If you want the ID at the first position in the ID sample, it is do-able.
>> It means perf tools will have to be changed to calculate the variable start
>> position of the ID sample, and then parse the ID sample forwards from there.
>> Please advise.
>
This is complicated and leads me to believe that a better way of doing this
is to leverage some bits in the header. This is what my proposal was. I did
not yet have a chance to post it. But you can use a bit in the header
to indicate
the presence of the eventID. That way, you do not have to relate to the
event attr->sample_type to determine how to parse the meta-data records
such as MMAP. When the bit is present in the header, the eventID is
to be found at -8 bytes form the end of the record.

> Oh urgh I see.. how about I merge something like the below first?
>
> Re-reading your patch; you add something to struct sample_id; which means that
> events which 'forget' to set perf_event_attr::sample_id_all while setting
> PERF_SAMPLE_IDENTIFIER are 'funny'. Should we refuse them?
>
>
> ---
> Subject: perf: Update perf_event_type documentation
>
> Due to a discussion with Adrian I had a good look at the perf_event_type record
> layout and found the documentation to be somewhat unclear.
>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> include/uapi/linux/perf_event.h | 21 +++++++++++++++++++--
> kernel/events/core.c | 31 ++++++++++++++++---------------
> 2 files changed, 35 insertions(+), 17 deletions(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 0b1df41..335016c 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -478,6 +478,16 @@ enum perf_event_type {
> * file will be supported by older perf tools, with these new optional
> * fields being ignored.
> *
> + * struct sample_id {
> + * { u32 pid, tid; } && PERF_SAMPLE_TID
> + * { u64 time; } && PERF_SAMPLE_TIME
> + * { u64 id; } && PERF_SAMPLE_ID
> + * { u64 stream_id;} && PERF_SAMPLE_STREAM_ID
> + * { u32 cpu, res; } && PERF_SAMPLE_CPU
> + * } && perf_event_attr::sample_id_all
> + */
> +
> + /*
> * The MMAP events record the PROT_EXEC mappings so that we can
> * correlate userspace IPs to code. They have the following structure:
> *
> @@ -488,7 +498,8 @@ enum perf_event_type {
> * u64 addr;
> * u64 len;
> * u64 pgoff;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_MMAP = 1,
> @@ -498,6 +509,7 @@ enum perf_event_type {
> * struct perf_event_header header;
> * u64 id;
> * u64 lost;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_LOST = 2,
> @@ -508,6 +520,7 @@ enum perf_event_type {
> *
> * u32 pid, tid;
> * char comm[];
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_COMM = 3,
> @@ -518,6 +531,7 @@ enum perf_event_type {
> * u32 pid, ppid;
> * u32 tid, ptid;
> * u64 time;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_EXIT = 4,
> @@ -528,6 +542,7 @@ enum perf_event_type {
> * u64 time;
> * u64 id;
> * u64 stream_id;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_THROTTLE = 5,
> @@ -539,6 +554,7 @@ enum perf_event_type {
> * u32 pid, ppid;
> * u32 tid, ptid;
> * u64 time;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_FORK = 7,
> @@ -549,6 +565,7 @@ enum perf_event_type {
> * u32 pid, tid;
> *
> * struct read_format values;
> + * struct sample_id sample_id;
> * };
> */
> PERF_RECORD_READ = 8,
> @@ -596,7 +613,7 @@ enum perf_event_type {
> * u64 dyn_size; } && PERF_SAMPLE_STACK_USER
> *
> * { u64 weight; } && PERF_SAMPLE_WEIGHT
> - * { u64 data_src; } && PERF_SAMPLE_DATA_SRC
> + * { u64 data_src; } && PERF_SAMPLE_DATA_SRC
> * };
> */
> PERF_RECORD_SAMPLE = 9,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 708ab70..c9ef899 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4462,20 +4462,6 @@ void perf_output_sample(struct perf_output_handle *handle,
> }
> }
>
> - if (!event->attr.watermark) {
> - int wakeup_events = event->attr.wakeup_events;
> -
> - if (wakeup_events) {
> - struct ring_buffer *rb = handle->rb;
> - int events = local_inc_return(&rb->events);
> -
> - if (events >= wakeup_events) {
> - local_sub(wakeup_events, &rb->events);
> - local_inc(&rb->wakeup);
> - }
> - }
> - }
> -
> if (sample_type & PERF_SAMPLE_BRANCH_STACK) {
> if (data->br_stack) {
> size_t size;
> @@ -4511,16 +4497,31 @@ void perf_output_sample(struct perf_output_handle *handle,
> }
> }
>
> - if (sample_type & PERF_SAMPLE_STACK_USER)
> + if (sample_type & PERF_SAMPLE_STACK_USER) {
> perf_output_sample_ustack(handle,
> data->stack_user_size,
> data->regs_user.regs);
> + }
>
> if (sample_type & PERF_SAMPLE_WEIGHT)
> perf_output_put(handle, data->weight);
>
> if (sample_type & PERF_SAMPLE_DATA_SRC)
> perf_output_put(handle, data->data_src.val);
> +
> + if (!event->attr.watermark) {
> + int wakeup_events = event->attr.wakeup_events;
> +
> + if (wakeup_events) {
> + struct ring_buffer *rb = handle->rb;
> + int events = local_inc_return(&rb->events);
> +
> + if (events >= wakeup_events) {
> + local_sub(wakeup_events, &rb->events);
> + local_inc(&rb->wakeup);
> + }
> + }
> + }
> }
>
> void perf_prepare_sample(struct perf_event_header *header,
>


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