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SubjectRe: [RFC PATCH 07/17] perf: Add pmu_info to user page
On Tue, Sep 05, 2017 at 04:30:16PM +0300, Alexander Shishkin wrote:
> Allow PMUs to supply additional static information that may be required
> by their decoders. Most of what Intel PT driver exports as capability
> attributes (timing packet freqencies, frequency ratios etc), its decoder
> needs to be able to correctly decode its binary stream. However, when
> decoding Intel PT stream from a core dump, we can't rely on the sysfs
> attributes, so we need to pack this information into the perf buffer,
> so that the resulting core dump is self-contained.
>
> In order to do this, we append a PMU-specific structure to the user
> page. Such structures will include size, for versioning.
>

> @@ -508,6 +513,18 @@ struct perf_addr_filters_head {
> unsigned int nr_file_filters;
> };
>
> +struct pmu_info {
> + /*
> + * Size of this structure, for versioning.
> + */
> + u32 note_size;
> +
> + /*
> + * Size of the container structure, not including this one
> + */
> + u32 pmu_descsz;
> +};
> +
> /**
> * enum perf_event_active_state - the states of a event
> */
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 3d64d9ea80..4cdd4fab9d 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -599,6 +599,16 @@ struct perf_event_mmap_page {
> __u64 aux_tail;
> __u64 aux_offset;
> __u64 aux_size;
> +
> + /*
> + * PMU data: static info that (AUX) decoder wants to know in order to
> + * decode correctly:
> + *
> + * pmu_offset >= sizeof(struct perf_event_mmap_page)
> + * pmu_offset + pmu_size <= PAGE_SIZE
> + */
> + __u64 pmu_offset;
> + __u64 pmu_size;
> };

Why like this? Why not dump the data as part of
PERF_RECORD_ITRACE_START/PERF_RECORD_AUX ?

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