[PATCH v6 04/10] libperf: Add evsel mmap support

Rob Herring
2021-03-11T00:10:58Z

In order to support usersapce access, an event must be mmapped. While
there's already mmap support for evlist, the usecase is a bit different
than the self monitoring with userspace access. So let's add a new
perf_evsel__mmap() function to mmap an evsel. This allows implementing
userspace access as a fastpath for perf_evsel__read().

The mmapped address is returned by perf_evsel__mmap_base() which
primarily for users/tests to check if userspace access is enabled.

Signed-off-by: Rob Herring <robh@kernel.org>
---
v6:
- split mmap struct into it's own xyarray
v5:
- Create an mmap for every underlying event opened. Due to this, we
need a different way to get the mmap ptr, so perf_evsel__mmap_base()
is introduced.
v4:
- Change perf_evsel__mmap size to pages instead of bytes
v3:
- New patch split out from user access patch
---
tools/lib/perf/Documentation/libperf.txt | 2 +
tools/lib/perf/evsel.c | 51 ++++++++++++++++++++++++
tools/lib/perf/include/internal/evsel.h | 1 +
tools/lib/perf/include/perf/evsel.h | 2 +
tools/lib/perf/libperf.map | 2 +
5 files changed, 58 insertions(+)

diff --git a/tools/lib/perf/Documentation/libperf.txt b/tools/lib/perf/Documentation/libperf.txt
index 0c74c30ed23a..a2c73df191ca 100644
--- a/tools/lib/perf/Documentation/libperf.txt
+++ b/tools/lib/perf/Documentation/libperf.txt
@@ -136,6 +136,8 @@ SYNOPSIS
struct perf_thread_map *threads);
void perf_evsel__close(struct perf_evsel *evsel);
void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu);
+ int perf_evsel__mmap(struct perf_evsel *evsel, int pages);
+ void *perf_evsel__mmap_base(struct perf_evsel *evsel, int cpu, int thread);
int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
struct perf_counts_values *count);
int perf_evsel__enable(struct perf_evsel *evsel);
diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
index 4dc06289f4c7..1057e9b15528 100644
--- a/tools/lib/perf/evsel.c
+++ b/tools/lib/perf/evsel.c
@@ -11,10 +11,12 @@
#include <stdlib.h>
#include <internal/xyarray.h>
#include <internal/cpumap.h>
+#include <internal/mmap.h>
#include <internal/threadmap.h>
#include <internal/lib.h>
#include <linux/string.h>
#include <sys/ioctl.h>
+#include <sys/mman.h>

void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr)
{
@@ -38,6 +40,7 @@ void perf_evsel__delete(struct perf_evsel *evsel)
}

#define FD(e, x, y) (*(int *) xyarray__entry(e->fd, x, y))
+#define MMAP(e, x, y) (e->mmap ? ((struct perf_mmap *) xyarray__entry(e->mmap, x, y)) : NULL)

int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)
{
@@ -55,6 +58,13 @@ int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)
return evsel->fd != NULL ? 0 : -ENOMEM;
}

+static int perf_evsel__alloc_mmap(struct perf_evsel *evsel, int ncpus, int nthreads)
+{
+ evsel->mmap = xyarray__new(ncpus, nthreads, sizeof(struct perf_mmap));
+
+ return evsel->mmap != NULL ? 0 : -ENOMEM;
+}
+
static int
sys_perf_event_open(struct perf_event_attr *attr,
pid_t pid, int cpu, int group_fd,
@@ -137,6 +147,8 @@ void perf_evsel__free_fd(struct perf_evsel *evsel)
{
xyarray__delete(evsel->fd);
evsel->fd = NULL;
+ xyarray__delete(evsel->mmap);
+ evsel->mmap = NULL;
}

void perf_evsel__close(struct perf_evsel *evsel)
@@ -156,6 +168,45 @@ void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu)
perf_evsel__close_fd_cpu(evsel, cpu);
}

+int perf_evsel__mmap(struct perf_evsel *evsel, int pages)
+{
+ int ret, cpu, thread;
+ struct perf_mmap_param mp = {
+ .prot = PROT_READ | PROT_WRITE,
+ .mask = (pages * page_size) - 1,
+ };
+
+ if (evsel->mmap == NULL &&
+ perf_evsel__alloc_mmap(evsel, xyarray__max_x(evsel->fd), xyarray__max_y(evsel->fd)) < 0)
+ return -ENOMEM;
+
+ for (cpu = 0; cpu < xyarray__max_x(evsel->fd); cpu++) {
+ for (thread = 0; thread < xyarray__max_y(evsel->fd); thread++) {
+ int fd = FD(evsel, cpu, thread);
+ struct perf_mmap *map = MMAP(evsel, cpu, thread);
+
+ if (fd < 0)
+ continue;
+
+ perf_mmap__init(map, NULL, false, NULL);
+
+ ret = perf_mmap__mmap(map, &mp, fd, cpu);
+ if (ret)
+ return -1;
+ }
+ }
+
+ return 0;
+}
+
+void *perf_evsel__mmap_base(struct perf_evsel *evsel, int cpu, int thread)
+{
+ if (FD(evsel, cpu, thread) < 0 || MMAP(evsel, cpu, thread) == NULL)
+ return NULL;
+
+ return MMAP(evsel, cpu, thread)->base;
+}
+
int perf_evsel__read_size(struct perf_evsel *evsel)
{
u64 read_format = evsel->attr.read_format;
diff --git a/tools/lib/perf/include/internal/evsel.h b/tools/lib/perf/include/internal/evsel.h
index 1ffd083b235e..1c067d088bc6 100644
--- a/tools/lib/perf/include/internal/evsel.h
+++ b/tools/lib/perf/include/internal/evsel.h
@@ -41,6 +41,7 @@ struct perf_evsel {
struct perf_cpu_map *own_cpus;
struct perf_thread_map *threads;
struct xyarray *fd;
+ struct xyarray *mmap;
struct xyarray *sample_id;
u64 *id;
u32 ids;
diff --git a/tools/lib/perf/include/perf/evsel.h b/tools/lib/perf/include/perf/evsel.h
index c82ec39a4ad0..9f5265f2f39f 100644
--- a/tools/lib/perf/include/perf/evsel.h
+++ b/tools/lib/perf/include/perf/evsel.h
@@ -27,6 +27,8 @@ LIBPERF_API int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *
struct perf_thread_map *threads);
LIBPERF_API void perf_evsel__close(struct perf_evsel *evsel);
LIBPERF_API void perf_evsel__close_cpu(struct perf_evsel *evsel, int cpu);
+LIBPERF_API int perf_evsel__mmap(struct perf_evsel *evsel, int pages);
+LIBPERF_API void *perf_evsel__mmap_base(struct perf_evsel *evsel, int cpu, int thread);
LIBPERF_API int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
struct perf_counts_values *count);
LIBPERF_API int perf_evsel__enable(struct perf_evsel *evsel);
diff --git a/tools/lib/perf/libperf.map b/tools/lib/perf/libperf.map
index 7be1af8a546c..0b993de15830 100644
--- a/tools/lib/perf/libperf.map
+++ b/tools/lib/perf/libperf.map
@@ -23,6 +23,8 @@ LIBPERF_0.0.1 {
perf_evsel__disable;
perf_evsel__open;
perf_evsel__close;
+ perf_evsel__mmap;
+ perf_evsel__mmap_base;
perf_evsel__read;
perf_evsel__cpus;
perf_evsel__threads;
--
2.27.0