Re: [PATCH 12/15] perf tools: allow non-matching sample types

[Stephane Eranian]

On Mon, Jun 24, 2013 at 3:16 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> Sample types need not be identical to determine
> the sample id from the event.  Only the position
> of the sample id needs to be the same.
>
> Compatible sample types are ones in which the bits
> defined by PERF_COMPAT_MASK are the same.
> 'perf_evlist__config()' forces sample types to be
> compatible on that basis.
>
This is indeed a major flaw of the current sampling buffer format.
I have a patch coming to address this from the kernel side.

I am trying to understand this patch and I am confused by the
description and especially the structure of COMPAT_MASK.

I agree that if the SAMPLE_ID position remains constant then
it can be extracted from the body of the sample uniformly.
The only way to guarantee a fixed position is by ensuring that
all the sample_types before SAMPLE_ID and either set or
unset. By before I don't mean in the enum order but in the
order in which the kernel lays them various sample_types
in the buffer. And that's determined by perf_output_sample().
So I don't understand why PERF_SAMPLE_CPU and
PERF_SAMPLE_STREAM_ID  are here.

Any explanation?


> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
>  tools/perf/util/event.h  |  6 ++++
>  tools/perf/util/evlist.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++--
>  tools/perf/util/evlist.h |  3 ++
>  tools/perf/util/evsel.c  | 41 +++++++++++++++++++++
>  tools/perf/util/evsel.h  |  4 +++
>  5 files changed, 145 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
> index 1813895..858572f 100644
> --- a/tools/perf/util/event.h
> +++ b/tools/perf/util/event.h
> @@ -65,6 +65,12 @@ struct read_event {
>         PERF_SAMPLE_ID | PERF_SAMPLE_STREAM_ID |        \
>          PERF_SAMPLE_CPU | PERF_SAMPLE_PERIOD)
>
> +#define PERF_COMPAT_MASK                               \
> +       (PERF_SAMPLE_IP   | PERF_SAMPLE_TID       |     \
> +        PERF_SAMPLE_TIME | PERF_SAMPLE_ADDR      |     \
> +        PERF_SAMPLE_ID   | PERF_SAMPLE_STREAM_ID |     \
> +        PERF_SAMPLE_CPU)
> +
>  struct sample_event {
>         struct perf_event_header        header;
>         u64 array[];
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index a660f56..85c4d91 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -49,10 +49,20 @@ struct perf_evlist *perf_evlist__new(void)
>         return evlist;
>  }
>
> +static void perf_evlist__set_id_pos(struct perf_evlist *evlist)
> +{
> +       struct perf_evsel *first = perf_evlist__first(evlist);
> +
> +       evlist->id_pos = first->id_pos;
> +       evlist->is_pos = first->is_pos;
> +}
> +
>  void perf_evlist__config(struct perf_evlist *evlist,
>                         struct perf_record_opts *opts)
>  {
>         struct perf_evsel *evsel;
> +       u64 compat = 0;
> +
>         /*
>          * Set the evsel leader links before we configure attributes,
>          * since some might depend on this info.
> @@ -68,7 +78,15 @@ void perf_evlist__config(struct perf_evlist *evlist,
>
>                 if (evlist->nr_entries > 1)
>                         perf_evsel__set_sample_id(evsel);
> +               compat |= evsel->attr.sample_type & PERF_COMPAT_MASK;
>         }
> +
> +       list_for_each_entry(evsel, &evlist->entries, node) {
> +               evsel->attr.sample_type |= compat;
> +               perf_evsel__calc_id_pos(evsel);
> +       }
> +
> +       perf_evlist__set_id_pos(evlist);
>  }
>
>  static void perf_evlist__purge(struct perf_evlist *evlist)
> @@ -102,6 +120,7 @@ void perf_evlist__add(struct perf_evlist *evlist, struct perf_evsel *entry)
>  {
>         list_add_tail(&entry->node, &evlist->entries);
>         ++evlist->nr_entries;
> +       perf_evlist__set_id_pos(evlist);
>  }
>
>  void perf_evlist__splice_list_tail(struct perf_evlist *evlist,
> @@ -110,6 +129,7 @@ void perf_evlist__splice_list_tail(struct perf_evlist *evlist,
>  {
>         list_splice_tail(list, &evlist->entries);
>         evlist->nr_entries += nr_entries;
> +       perf_evlist__set_id_pos(evlist);
>  }
>
>  void __perf_evlist__set_leader(struct list_head *list)
> @@ -339,6 +359,55 @@ struct perf_evsel *perf_evlist__id2evsel(struct perf_evlist *evlist, u64 id)
>         return NULL;
>  }
>
> +static int perf_evlist__event2id(struct perf_evlist *evlist,
> +                                union perf_event *event, u64 *id)
> +{
> +       const u64 *array = event->sample.array;
> +       ssize_t n;
> +
> +       n = (event->header.size - sizeof(event->header)) >> 3;
> +
> +       if (event->header.type == PERF_RECORD_SAMPLE) {
> +               if (evlist->id_pos >= n)
> +                       return -1;
> +               *id = array[evlist->id_pos];
> +       } else {
> +               if (evlist->is_pos >= n)
> +                       return -1;
> +               n -= evlist->is_pos;
> +               *id = array[n];
> +       }
> +       return 0;
> +}
> +
> +static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist,
> +                                                  union perf_event *event)
> +{
> +       struct hlist_head *head;
> +       struct perf_sample_id *sid;
> +       int hash;
> +       u64 id;
> +
> +       if (evlist->nr_entries == 1 || evlist->matching_sample_types)
> +               return perf_evlist__first(evlist);
> +
> +       if (perf_evlist__event2id(evlist, event, &id))
> +               return NULL;
> +
> +       /* Synthesized events have an id of zero */
> +       if (!id)
> +               return perf_evlist__first(evlist);
> +
> +       hash = hash_64(id, PERF_EVLIST__HLIST_BITS);
> +       head = &evlist->heads[hash];
> +
> +       hlist_for_each_entry(sid, head, node) {
> +               if (sid->id == id)
> +                       return sid->evsel;
> +       }
> +       return NULL;
> +}
> +
>  union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx)
>  {
>         struct perf_mmap *md = &evlist->mmap[idx];
> @@ -650,9 +719,26 @@ int perf_evlist__set_filter(struct perf_evlist *evlist, const char *filter)
>  bool perf_evlist__valid_sample_type(struct perf_evlist *evlist)
>  {
>         struct perf_evsel *first = perf_evlist__first(evlist), *pos = first;
> +       bool ok = true;
>
>         list_for_each_entry_continue(pos, &evlist->entries, node) {
> -               if (first->attr.sample_type != pos->attr.sample_type)
> +               if (first->attr.sample_type != pos->attr.sample_type) {
> +                       ok = false;
> +                       break;
> +               }
> +       }
> +
> +       if (ok) {
> +               evlist->matching_sample_types = true;
> +               return true;
> +       }
> +
> +       if (evlist->id_pos < 0 || evlist->is_pos < 0)
> +               return false;
> +
> +       list_for_each_entry(pos, &evlist->entries, node) {
> +               if (pos->id_pos != evlist->id_pos ||
> +                   pos->is_pos != evlist->is_pos)
>                         return false;
>         }
>
> @@ -848,7 +934,10 @@ int perf_evlist__start_workload(struct perf_evlist *evlist)
>  int perf_evlist__parse_sample(struct perf_evlist *evlist, union perf_event *event,
>                               struct perf_sample *sample)
>  {
> -       struct perf_evsel *evsel = perf_evlist__first(evlist);
> +       struct perf_evsel *evsel = perf_evlist__event2evsel(evlist, event);
> +
> +       if (!evsel)
> +               return -EFAULT;
>         return perf_evsel__parse_sample(evsel, event, sample);
>  }
>
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 0583d36..bfcbf67 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -32,11 +32,14 @@ struct perf_evlist {
>         int              nr_fds;
>         int              nr_mmaps;
>         int              mmap_len;
> +       int              id_pos;
> +       int              is_pos;
>         struct {
>                 int     cork_fd;
>                 pid_t   pid;
>         } workload;
>         bool             overwrite;
> +       bool             matching_sample_types;
>         struct perf_mmap *mmap;
>         struct pollfd    *pollfd;
>         struct thread_map *threads;
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index d01d2cd..ee0f894 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -46,6 +46,46 @@ static int __perf_evsel__sample_size(u64 sample_type)
>         return size;
>  }
>
> +static int __perf_evsel__calc_id_pos(u64 sample_type)
> +{
> +       u64 mask;
> +       int i, idx;
> +
> +       if (!(sample_type & PERF_SAMPLE_ID))
> +               return -1;
> +
> +       mask = sample_type & (PERF_SAMPLE_ID - 1);
> +
> +       for (i = 0, idx = 0; i < 64; i++) {
> +               if (mask & (1ULL << i))
> +                       idx++;
> +       }
> +
> +       return idx;
> +}
> +
> +static int __perf_evsel__calc_is_pos(u64 sample_type)
> +{
> +       int idx = 1;
> +
> +       if (!(sample_type & PERF_SAMPLE_ID))
> +               return -1;
> +
> +       if (sample_type & PERF_SAMPLE_CPU)
> +               idx += 1;
> +
> +       if (sample_type & PERF_SAMPLE_STREAM_ID)
> +               idx += 1;
> +
> +       return idx;
> +}
> +
> +void perf_evsel__calc_id_pos(struct perf_evsel *evsel)
> +{
> +       evsel->id_pos = __perf_evsel__calc_id_pos(evsel->attr.sample_type);
> +       evsel->is_pos = __perf_evsel__calc_is_pos(evsel->attr.sample_type);
> +}
> +
>  void hists__init(struct hists *hists)
>  {
>         memset(hists, 0, sizeof(*hists));
> @@ -89,6 +129,7 @@ void perf_evsel__init(struct perf_evsel *evsel,
>         INIT_LIST_HEAD(&evsel->node);
>         hists__init(&evsel->hists);
>         evsel->sample_size = __perf_evsel__sample_size(attr->sample_type);
> +       perf_evsel__calc_id_pos(evsel);
>  }
>
>  struct perf_evsel *perf_evsel__new(struct perf_event_attr *attr, int idx)
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 3f156cc..88b4319 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -71,6 +71,8 @@ struct perf_evsel {
>         } handler;
>         struct cpu_map          *cpus;
>         unsigned int            sample_size;
> +       int                     id_pos;
> +       int                     is_pos;
>         bool                    supported;
>         bool                    needs_swap;
>         /* parse modifier helper */
> @@ -100,6 +102,8 @@ void perf_evsel__delete(struct perf_evsel *evsel);
>  void perf_evsel__config(struct perf_evsel *evsel,
>                         struct perf_record_opts *opts);
>
> +void perf_evsel__calc_id_pos(struct perf_evsel *evsel);
> +
>  bool perf_evsel__is_cache_op_valid(u8 type, u8 op);
>
>  #define PERF_EVSEL__MAX_ALIASES 8
> --
> 1.7.11.7
>
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