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Message-ID: <CAEf4BzaL71O-odNtE88OwwZcVkRPw2uRaBgRAZYcoVo+G+38Mg@mail.gmail.com>
Date: Wed, 6 Nov 2024 11:36:19 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Ian Rogers <irogers@...gle.com>,
Kan Liang <kan.liang@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org, Song Liu <song@...nel.org>, bpf@...r.kernel.org,
Stephane Eranian <eranian@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, Kees Cook <kees@...nel.org>,
Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>
Subject: Re: [PATCH 2/4] perf lock contention: Run BPF slab cache iterator
On Tue, Nov 5, 2024 at 9:27 AM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Recently the kernel got the kmem_cache iterator to traverse metadata of
> slab objects. This can be used to symbolize dynamic locks in a slab.
>
> The new slab_caches hash map will have the pointer of the kmem_cache as
> a key and save the name and a id. The id will be saved in the flags
> part of the lock.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> tools/perf/util/bpf_lock_contention.c | 51 +++++++++++++++++++
> .../perf/util/bpf_skel/lock_contention.bpf.c | 28 ++++++++++
> tools/perf/util/bpf_skel/lock_data.h | 12 +++++
> tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 8 +++
> 4 files changed, 99 insertions(+)
>
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index 41a1ad08789511c3..a2efd40897bad316 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -12,12 +12,60 @@
> #include <linux/zalloc.h>
> #include <linux/string.h>
> #include <bpf/bpf.h>
> +#include <bpf/btf.h>
> #include <inttypes.h>
>
> #include "bpf_skel/lock_contention.skel.h"
> #include "bpf_skel/lock_data.h"
>
> static struct lock_contention_bpf *skel;
> +static bool has_slab_iter;
> +
> +static void check_slab_cache_iter(struct lock_contention *con)
> +{
> + struct btf *btf = btf__load_vmlinux_btf();
> + s32 ret;
> +
> + ret = libbpf_get_error(btf);
please don't use libbpf_get_error() in new code. I left that API for
cases when user might want to support both per-1.0 libbpf and 1.0+,
but by now I don't think you should be caring about <1.0 versions. And
in 1.0+, you'll get btf == NULL on error, and errno will be set to
error. So just check errno directly.
> + if (ret) {
> + pr_debug("BTF loading failed: %d\n", ret);
> + return;
> + }
> +
> + ret = btf__find_by_name_kind(btf, "bpf_iter__kmem_cache", BTF_KIND_STRUCT);
> + if (ret < 0) {
> + bpf_program__set_autoload(skel->progs.slab_cache_iter, false);
> + pr_debug("slab cache iterator is not available: %d\n", ret);
> + goto out;
> + }
> +
> + has_slab_iter = true;
> +
> + bpf_map__set_max_entries(skel->maps.slab_caches, con->map_nr_entries);
> +out:
> + btf__free(btf);
> +}
> +
> +static void run_slab_cache_iter(void)
> +{
> + int fd;
> + char buf[256];
> +
> + if (!has_slab_iter)
> + return;
> +
> + fd = bpf_iter_create(bpf_link__fd(skel->links.slab_cache_iter));
> + if (fd < 0) {
> + pr_debug("cannot create slab cache iter: %d\n", fd);
> + return;
> + }
> +
> + /* This will run the bpf program */
> + while (read(fd, buf, sizeof(buf)) > 0)
> + continue;
> +
> + close(fd);
> +}
>
> int lock_contention_prepare(struct lock_contention *con)
> {
> @@ -109,6 +157,8 @@ int lock_contention_prepare(struct lock_contention *con)
> skel->rodata->use_cgroup_v2 = 1;
> }
>
> + check_slab_cache_iter(con);
> +
> if (lock_contention_bpf__load(skel) < 0) {
> pr_err("Failed to load lock-contention BPF skeleton\n");
> return -1;
> @@ -304,6 +354,7 @@ static void account_end_timestamp(struct lock_contention *con)
>
> int lock_contention_start(void)
> {
> + run_slab_cache_iter();
> skel->bss->enabled = 1;
> return 0;
> }
> diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> index 1069bda5d733887f..fd24ccb00faec0ba 100644
> --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
> +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
> @@ -100,6 +100,13 @@ struct {
> __uint(max_entries, 1);
> } cgroup_filter SEC(".maps");
>
> +struct {
> + __uint(type, BPF_MAP_TYPE_HASH);
> + __uint(key_size, sizeof(long));
> + __uint(value_size, sizeof(struct slab_cache_data));
> + __uint(max_entries, 1);
> +} slab_caches SEC(".maps");
> +
> struct rw_semaphore___old {
> struct task_struct *owner;
> } __attribute__((preserve_access_index));
> @@ -136,6 +143,8 @@ int perf_subsys_id = -1;
>
> __u64 end_ts;
>
> +__u32 slab_cache_id;
> +
> /* error stat */
> int task_fail;
> int stack_fail;
> @@ -563,4 +572,23 @@ int BPF_PROG(end_timestamp)
> return 0;
> }
>
> +SEC("iter/kmem_cache")
> +int slab_cache_iter(struct bpf_iter__kmem_cache *ctx)
> +{
> + struct kmem_cache *s = ctx->s;
> + struct slab_cache_data d;
> +
> + if (s == NULL)
> + return 0;
> +
> + d.id = ++slab_cache_id << LCB_F_SLAB_ID_SHIFT;
> + bpf_probe_read_kernel_str(d.name, sizeof(d.name), s->name);
> +
> + if (d.id >= LCB_F_SLAB_ID_END)
> + return 0;
> +
> + bpf_map_update_elem(&slab_caches, &s, &d, BPF_NOEXIST);
> + return 0;
> +}
> +
> char LICENSE[] SEC("license") = "Dual BSD/GPL";
> diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
> index 4f0aae5483745dfa..c15f734d7fc4aecb 100644
> --- a/tools/perf/util/bpf_skel/lock_data.h
> +++ b/tools/perf/util/bpf_skel/lock_data.h
> @@ -32,9 +32,16 @@ struct contention_task_data {
> #define LCD_F_MMAP_LOCK (1U << 31)
> #define LCD_F_SIGHAND_LOCK (1U << 30)
>
> +#define LCB_F_SLAB_ID_SHIFT 16
> +#define LCB_F_SLAB_ID_START (1U << 16)
> +#define LCB_F_SLAB_ID_END (1U << 26)
> +#define LCB_F_SLAB_ID_MASK 0x03FF0000U
> +
> #define LCB_F_TYPE_MAX (1U << 7)
> #define LCB_F_TYPE_MASK 0x0000007FU
>
> +#define SLAB_NAME_MAX 28
> +
> struct contention_data {
> u64 total_time;
> u64 min_time;
> @@ -55,4 +62,9 @@ enum lock_class_sym {
> LOCK_CLASS_RQLOCK,
> };
>
> +struct slab_cache_data {
> + u32 id;
> + char name[SLAB_NAME_MAX];
> +};
> +
> #endif /* UTIL_BPF_SKEL_LOCK_DATA_H */
> diff --git a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> index 4dcad7b682bdee9c..7b81d3173917fdb5 100644
> --- a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> +++ b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> @@ -195,4 +195,12 @@ struct bpf_perf_event_data_kern {
> */
> struct rq {};
>
> +struct kmem_cache {
> + const char *name;
> +} __attribute__((preserve_access_index));
> +
> +struct bpf_iter__kmem_cache {
> + struct kmem_cache *s;
> +} __attribute__((preserve_access_index));
> +
> #endif // __VMLINUX_H
> --
> 2.47.0.199.ga7371fff76-goog
>
>
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