Re: [PATCH v7 2/4] libperf: Add evsel mmap support

From: Arnaldo Carvalho de Melo
Date: Tue Apr 13 2021 - 14:39:30 EST

Em Tue, Apr 13, 2021 at 12:16:04PM -0500, Rob Herring escreveu:
> 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@xxxxxxxxxx>
> ---
> v7:
> - Add NULL fd check to perf_evsel__mmap
> 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 | 54 ++++++++++++++++++++++++
> 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, 61 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..7e140763552f 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 +168,48 @@ 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->fd == NULL)
> + return -EINVAL;
> +
> + 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;
> +}

Where is the counterpart? I.e. perf_evsel__munmap(), and it should be
called if perf_evsel__mmap() fails, right?

- Arnaldo

> +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
>

--

- Arnaldo