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Message-ID: <Zy0PT0apgXWnBglI@google.com>
Date: Thu, 7 Nov 2024 11:04:47 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
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
Hello,
On Wed, Nov 06, 2024 at 11:36:19AM -0800, Andrii Nakryiko wrote:
> 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.
Oh, great. I'll update the code like below.
if (btf == NULL) {
pr_debug("BTF loading failed: %s\n", strerror(errno));
return;
}
Thanks for your review,
Namhyung
>
> > + 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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