Re: [PATCH v6 1/7] perf util: Create streams

Arnaldo Carvalho de Melo
2020-09-17T20:21:05Z

Em Fri, Sep 11, 2020 at 04:03:47PM +0800, Jin Yao escreveu:
> We define the stream is the branch history which is aggregated by
> the branch records from perf samples. For example, the callchains
> aggregated from the branch records are considered as streams.
> By browsing the hot stream, we can understand the hot code path.
>
> Now we only support the callchain for stream. For measuring the
> hot level for a stream, we use the callchain_node->hit, higher
> is hotter.
>
> There may be many callchains sampled so we only focus on the top
> N hottest callchains. N is a user defined parameter or predefined
> default value (nr_streams_max).
>
> This patch creates an evsel_streams array per event, and saves
> the top N hottest streams in a stream array.
>
> So now we can get the per-event top N hottest streams.
>
> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
> ---
> v6:
> - Rebase to perf/core
>
> v5:
> - Remove enum stram_type
> - Rebase to perf/core
>
> v4:
> - Refactor the code
> - Rename patch name from 'perf util: Create streams for managing
> top N hottest callchains' to 'perf util: Create streams'
>
> v2:
> - Use zfree in free_evsel_streams().
>
> tools/perf/util/Build | 1 +
> tools/perf/util/stream.c | 148 +++++++++++++++++++++++++++++++++++++++
> tools/perf/util/stream.h | 23 ++++++
> 3 files changed, 172 insertions(+)
> create mode 100644 tools/perf/util/stream.c
> create mode 100644 tools/perf/util/stream.h
>
> diff --git a/tools/perf/util/Build b/tools/perf/util/Build
> index cd5e41960e64..6ffdf833cd51 100644
> --- a/tools/perf/util/Build
> +++ b/tools/perf/util/Build
> @@ -101,6 +101,7 @@ perf-y += call-path.o
> perf-y += rwsem.o
> perf-y += thread-stack.o
> perf-y += spark.o
> +perf-y += stream.o
> perf-$(CONFIG_AUXTRACE) += auxtrace.o
> perf-$(CONFIG_AUXTRACE) += intel-pt-decoder/
> perf-$(CONFIG_AUXTRACE) += intel-pt.o
> diff --git a/tools/perf/util/stream.c b/tools/perf/util/stream.c
> new file mode 100644
> index 000000000000..015c1d07ce3a
> --- /dev/null
> +++ b/tools/perf/util/stream.c
> @@ -0,0 +1,148 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Compare and figure out the top N hottest streams
> + * Copyright (c) 2020, Intel Corporation.
> + * Author: Jin Yao
> + */
> +
> +#include <inttypes.h>
> +#include <stdlib.h>
> +#include <linux/zalloc.h>
> +#include "debug.h"
> +#include "hist.h"
> +#include "sort.h"
> +#include "stream.h"
> +#include "evlist.h"
> +
> +static void free_evsel_streams(struct evsel_streams *es, int nr_evsel)

Please name the functions with the struct name first, followed by __ and
then the method name, i.e. for this one:

static void evsel_streams__delete(struct evsel_streams *es, int nr_evsels)

One thing that made me curious is why nr_evsels (plural please) isn't in
'struct evsel_streams', why?

> +{
> + for (int i = 0; i < nr_evsel; i++)
> + zfree(&es[i].streams);
> +
> + free(es);
> +}
> +
> +static struct evsel_streams *create_evsel_streams(int nr_evsel,
> + int nr_streams_max)

Oh, I see, you create just an array :-\

Please rename it to:

evsel_streams__new(int nr_evsels, int nr_streams_max)

> +{
> + struct evsel_streams *es;
> +
> + es = calloc(nr_evsel, sizeof(struct evsel_streams));
> + if (!es)
> + return NULL;
> +
> + for (int i = 0; i < nr_evsel; i++) {
> + struct evsel_streams *s = &es[i];
> +
> + s->streams = calloc(nr_streams_max, sizeof(struct stream));
> + if (!s->streams)
> + goto err;
> +
> + s->nr_streams_max = nr_streams_max;
> + s->evsel_idx = -1;
> + }
> +
> + return es;
> +
> +err:
> + free_evsel_streams(es, nr_evsel);
> + return NULL;
> +}
> +
> +/*
> + * The cnodes with high hit number are hot callchains.
> + */
> +static void set_hot_cnode(struct evsel_streams *es,
> + struct callchain_node *cnode)

Since it is static its kinda ok not to have the prefix, but I'd do it
as:

static void evsel_streams__set_hot_cnode(...)

For ctags sake, for instance, i.e. navigate in vim using ctags.

> +{
> + int i, idx = 0;
> + u64 hit;
> +
> + if (es->nr_streams < es->nr_streams_max) {
> + i = es->nr_streams;
> + es->streams[i].cnode = cnode;
> + es->nr_streams++;
> + return;
> + }
> +
> + /*
> + * Considering a few number of hot streams, only use simple
> + * way to find the cnode with smallest hit number and replace.
> + */
> + hit = (es->streams[0].cnode)->hit;
> + for (i = 1; i < es->nr_streams; i++) {
> + if ((es->streams[i].cnode)->hit < hit) {
> + hit = (es->streams[i].cnode)->hit;
> + idx = i;
> + }
> + }
> +
> + if (cnode->hit > hit)
> + es->streams[idx].cnode = cnode;
> +}
> +
> +static void update_hot_callchain(struct hist_entry *he,
> + struct evsel_streams *es)
> +{
> + struct rb_root *root = &he->sorted_chain;
> + struct rb_node *rb_node = rb_first(root);
> + struct callchain_node *cnode;
> +
> + while (rb_node) {
> + cnode = rb_entry(rb_node, struct callchain_node, rb_node);
> + set_hot_cnode(es, cnode);
> + rb_node = rb_next(rb_node);
> + }
> +}
> +
> +static void init_hot_callchain(struct hists *hists, struct evsel_streams *es)
> +{
> + struct rb_node *next = rb_first_cached(&hists->entries);
> +
> + while (next) {
> + struct hist_entry *he;
> +
> + he = rb_entry(next, struct hist_entry, rb_node);
> + update_hot_callchain(he, es);
> + next = rb_next(&he->rb_node);
> + }
> +}
> +
> +static int evlist_init_callchain_streams(struct evlist *evlist,
> + struct evsel_streams *es, int nr_es)

So here we miss just one extra _, i.e.:

+static int evlist__init_callchain_streams(struct evlist *evlist,
+ struct evsel_streams *es, int nr_es)

> +{
> + struct evsel *pos;
> + int i = 0;
> +
> + BUG_ON(nr_es < evlist->core.nr_entries);
> +
> + evlist__for_each_entry(evlist, pos) {
> + struct hists *hists = evsel__hists(pos);
> +
> + hists__output_resort(hists, NULL);
> + init_hot_callchain(hists, &es[i]);
> + es[i].evsel_idx = pos->idx;
> + i++;
> + }
> +
> + return 0;
> +}
> +
> +struct evsel_streams *perf_evlist__create_streams(struct evlist *evlist,
> + int nr_streams_max)

And here it should be:

+struct evsel_streams *evlist__create_streams(struct evlist *evlist,
+ int nr_streams_max)

I.e. without the perf_ prefix, since that is for 'struct perf_evlist'
methods, that are in tools/lib/perf/, aka libperf

> +{
> + struct evsel_streams *es;
> + int nr_evsel = evlist->core.nr_entries, ret = -1;
> +
> + es = create_evsel_streams(nr_evsel, nr_streams_max);

Minor nitpick, usually combine declaration with first attribution, if
possible, i.e.:

+ struct evsel_streams *es = create_evsel_streams(nr_evsel, nr_streams_max);

> + if (!es)
> + return NULL;
> +
> + ret = evlist_init_callchain_streams(evlist, es, nr_evsel);
> + if (ret) {
> + free_evsel_streams(es, nr_evsel);
> + return NULL;
> + }
> +
> + return es;
> +}
> diff --git a/tools/perf/util/stream.h b/tools/perf/util/stream.h
> new file mode 100644
> index 000000000000..c6844c5787cb
> --- /dev/null
> +++ b/tools/perf/util/stream.h
> @@ -0,0 +1,23 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __PERF_STREAM_H
> +#define __PERF_STREAM_H
> +
> +#include "callchain.h"
> +
> +struct stream {
> + struct callchain_node *cnode;
> +};
> +
> +struct evsel_streams {
> + struct stream *streams;
> + int nr_streams_max;
> + int nr_streams;
> + int evsel_idx;
> +};
> +
> +struct evlist;
> +
> +struct evsel_streams *perf_evlist__create_streams(struct evlist *evlist,
> + int nr_streams_max);
> +

evlist__create_streams()

> +#endif /* __PERF_STREAM_H */
> --
> 2.17.1
>

--

- Arnaldo