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Date: Mon, 30 Aug 2010 13:13:47 +0100
From: Matt Fleming <matt@...sole-pimps.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Zhang Rui <rui.zhang@...el.com>, linux-kernel@...r.kernel.org,
Ingo Molnar <mingo@...e.hu>,
Frederic Weisbecker <fweisbec@...il.com>,
Robert Richter <robert.richter@....com>,
Lin Ming <ming.m.lin@...el.com>,
Paul Mackerras <paulus@...ba.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Don Zickus <dzickus@...hat.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Len Brown <lenb@...nel.org>,
Matthew Garrett <mjg59@...f.ucam.org>
Subject: [RFC][PATCH 5/5] perf: Add support for PERF_SAMPLE_READ samples
Using the counter values from PERF_SAMPLE_READ samples and weighting
them by the hrtimer period we can approximate a counter with a PMI. By
following how fast a counter varies over a hrtimer period we can figure
out which functions are causing the counters to change the fastest.
Suppose you have a workload consisting of two main parts:
my_important_work()
{
load_my_data();
compute_me_silly();
}
Now, lets assume that both these functions take the same time to
complete for each part of work. In that case a periodic timer generate
samples that are about 50/50 distributed between these two functions.
Now, let us further assume that load_my_data() is so slow because its
missing all the caches and compute_me_silly() is slow because its
defeating the branch predictor.
So what we end up with, is that when we sample for cache-misses we get
load_my_data() as the predominant function, not a nice 50/50
relation. Idem for branch misses and compute_me_silly().
By weighting the samples by the hw counter delta we get this, if we
assume that the sampling frequency is not a harmonic of the runtime of
these functions, then statistics will dtrt.
Signed-off-by: Matt Fleming <matt@...sole-pimps.org>
---
tools/perf/builtin-record.c | 70 ++++++++++++++++++++++++++++++++++++++-----
tools/perf/builtin-report.c | 19 ++++++++++-
tools/perf/util/event.c | 7 +++-
tools/perf/util/event.h | 15 +++++++++
4 files changed, 99 insertions(+), 12 deletions(-)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index b530bee..4bd7c4a 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -224,20 +224,43 @@ static struct perf_header_attr *get_header_attr(struct perf_event_attr *a, int n
return h_attr;
}
+struct read_format_single {
+ u64 count;
+ u64 time_enabled;
+ u64 time_running;
+ u64 id;
+};
+
+struct group_entry {
+ u64 value;
+ u64 id;
+};
+
+struct read_format_group {
+ u64 nr;
+ u64 time_enabled;
+ u64 time_running;
+ struct group_entry cntr[0];
+};
+
static void create_counter(int counter, int cpu)
{
char *filter = filters[counter];
struct perf_event_attr *attr = attrs + counter;
struct perf_header_attr *h_attr;
int track = !counter; /* only the first counter needs these */
+ size_t read_data_sz;
+ void *read_data;
int thread_index;
int ret;
- struct {
- u64 count;
- u64 time_enabled;
- u64 time_running;
- u64 id;
- } read_data;
+ u64 id;
+
+ read_data_sz = sizeof(struct read_format_single);
+ read_data = malloc(read_data_sz);
+ if (!read_data) {
+ perror("Unable to allocate read data");
+ return;
+ }
attr->read_format = PERF_FORMAT_TOTAL_TIME_ENABLED |
PERF_FORMAT_TOTAL_TIME_RUNNING |
@@ -325,6 +348,32 @@ try_again:
attr->config = PERF_COUNT_SW_CPU_CLOCK;
goto try_again;
}
+
+ /*
+ * If we requested a sampling counter but the
+ * hardware doesn't support it, create an
+ * event group.
+ */
+ if (err == EINVAL && attr->sample_period && !group) {
+ size_t sz = sizeof(struct read_format_group);
+
+ attr->read_format |= PERF_FORMAT_GROUP;
+ attr->sample_type |= PERF_SAMPLE_READ;
+
+ free(read_data);
+
+ read_data_sz = sz + (sizeof(struct group_entry) * nr_counters);
+ read_data = malloc(read_data_sz);
+ if (!read_data) {
+ perror("Unable to allocate read_data");
+ exit(-1);
+ }
+
+ /* Only try to fallback to a group once. */
+ group = 1;
+ goto try_again;
+ }
+
printf("\n");
error("perfcounter syscall returned with %d (%s)\n",
fd[nr_cpu][counter][thread_index], strerror(err));
@@ -352,12 +401,17 @@ try_again:
}
}
- if (read(fd[nr_cpu][counter][thread_index], &read_data, sizeof(read_data)) == -1) {
+ if (read(fd[nr_cpu][counter][thread_index], read_data, read_data_sz) == -1) {
perror("Unable to read perf file descriptor");
exit(-1);
}
- if (perf_header_attr__add_id(h_attr, read_data.id) < 0) {
+ if (attr->read_format & PERF_FORMAT_GROUP)
+ id = ((struct read_format_group *)read_data)->cntr[0].id;
+ else
+ id = ((struct read_format_single *)read_data)->id;
+
+ if (perf_header_attr__add_id(h_attr, id) < 0) {
pr_warning("Not enough memory to add id\n");
exit(-1);
}
diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 5de405d..44772fb 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -139,14 +139,29 @@ static int add_event_total(struct perf_session *session,
if (!hists)
return -ENOMEM;
- hists->stats.total_period += data->period;
+ if (attr && attr->type & PERF_SAMPLE_READ) {
+ u64 value;
+ unsigned int i;
+
+ for (i = 0; i < data->group->nr; i++) {
+ struct read_group_entry *entry = &data->group->entries[i];
+
+ value = entry->value * data->group->time_running;
+ hists->stats.total_period += value;
+ session->hists.stats.total_period += value;
+ }
+ } else {
+ hists->stats.total_period += data->period;
+ session->hists.stats.total_period += data->period;
+ }
+
/*
* FIXME: add_event_total should be moved from here to
* perf_session__process_event so that the proper hist is passed to
* the event_op methods.
*/
hists__inc_nr_events(hists, PERF_RECORD_SAMPLE);
- session->hists.stats.total_period += data->period;
+
return 0;
}
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index dab9e75..c52b3ef 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -816,8 +816,11 @@ int event__parse_sample(const event_t *event, u64 type, struct sample_data *data
}
if (type & PERF_SAMPLE_READ) {
- pr_debug("PERF_SAMPLE_READ is unsuported for now\n");
- return -1;
+ /* FIXME assume group read event for now. */
+ size_t entry_sz = sizeof(struct read_group_entry);
+
+ data->group = (struct read_group *)array;
+ array += sizeof(struct read_group) + (data->group->nr * entry_sz);
}
if (type & PERF_SAMPLE_CALLCHAIN) {
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 8e790da..e7cadaa 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -56,6 +56,20 @@ struct read_event {
u64 id;
};
+struct read_group_entry {
+ u64 value;
+ u64 id;
+};
+
+struct read_group {
+ struct perf_event_header header;
+ u32 pid, tid;
+ u64 nr;
+ u64 time_enabled;
+ u64 time_running;
+ struct read_group_entry entries[0];
+};
+
struct sample_event {
struct perf_event_header header;
u64 array[];
@@ -73,6 +87,7 @@ struct sample_data {
u32 raw_size;
void *raw_data;
struct ip_callchain *callchain;
+ struct read_group *group;
};
#define BUILD_ID_SIZE 20
--
1.7.1
--
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